diff --git a/src/main/java/org/qortal/transaction/CreateGroupTransaction.java b/src/main/java/org/qortal/transaction/CreateGroupTransaction.java
index 42c69541..0d4cbc12 100644
--- a/src/main/java/org/qortal/transaction/CreateGroupTransaction.java
+++ b/src/main/java/org/qortal/transaction/CreateGroupTransaction.java
@@ -77,6 +77,16 @@ public class CreateGroupTransaction extends Transaction {
 		if (createGroupTransactionData.getApprovalThreshold() == null)
 			return ValidationResult.INVALID_GROUP_APPROVAL_THRESHOLD;
 
+		// Check min/max block delay values
+		if (createGroupTransactionData.getMinimumBlockDelay() < 0)
+			return ValidationResult.INVALID_GROUP_BLOCK_DELAY;
+
+		if (createGroupTransactionData.getMaximumBlockDelay() < 1)
+			return ValidationResult.INVALID_GROUP_BLOCK_DELAY;
+
+		if (createGroupTransactionData.getMaximumBlockDelay() < createGroupTransactionData.getMinimumBlockDelay())
+			return ValidationResult.INVALID_GROUP_BLOCK_DELAY;
+
 		// Check group name size bounds
 		int groupNameLength = Utf8.encodedLength(createGroupTransactionData.getGroupName());
 		if (groupNameLength < 1 || groupNameLength > Group.MAX_NAME_SIZE)
diff --git a/src/main/java/org/qortal/transaction/Transaction.java b/src/main/java/org/qortal/transaction/Transaction.java
index 75e31f8c..69dd42d9 100644
--- a/src/main/java/org/qortal/transaction/Transaction.java
+++ b/src/main/java/org/qortal/transaction/Transaction.java
@@ -242,6 +242,7 @@ public abstract class Transaction {
 		ACCOUNT_CANNOT_REWARD_SHARE(90),
 		SELF_SHARE_EXISTS(91),
 		ACCOUNT_ALREADY_EXISTS(92),
+		INVALID_GROUP_BLOCK_DELAY(93),
 		NOT_YET_RELEASED(1000);
 
 		public final int value;
diff --git a/src/main/java/org/qortal/transaction/UpdateGroupTransaction.java b/src/main/java/org/qortal/transaction/UpdateGroupTransaction.java
index e25b0b57..26b35c36 100644
--- a/src/main/java/org/qortal/transaction/UpdateGroupTransaction.java
+++ b/src/main/java/org/qortal/transaction/UpdateGroupTransaction.java
@@ -83,6 +83,16 @@ public class UpdateGroupTransaction extends Transaction {
 		if (updateGroupTransactionData.getNewApprovalThreshold() == null)
 			return ValidationResult.INVALID_GROUP_APPROVAL_THRESHOLD;
 
+		// Check min/max block delay values
+		if (updateGroupTransactionData.getNewMinimumBlockDelay() < 0)
+			return ValidationResult.INVALID_GROUP_BLOCK_DELAY;
+
+		if (updateGroupTransactionData.getNewMaximumBlockDelay() < 1)
+			return ValidationResult.INVALID_GROUP_BLOCK_DELAY;
+
+		if (updateGroupTransactionData.getNewMaximumBlockDelay() < updateGroupTransactionData.getNewMinimumBlockDelay())
+			return ValidationResult.INVALID_GROUP_BLOCK_DELAY;
+
 		// Check new description size bounds
 		int newDescriptionLength = Utf8.encodedLength(updateGroupTransactionData.getNewDescription());
 		if (newDescriptionLength < 1 || newDescriptionLength > Group.MAX_DESCRIPTION_SIZE)
diff --git a/src/test/java/org/qortal/test/group/GroupBlockDelayTests.java b/src/test/java/org/qortal/test/group/GroupBlockDelayTests.java
new file mode 100644
index 00000000..1af2857f
--- /dev/null
+++ b/src/test/java/org/qortal/test/group/GroupBlockDelayTests.java
@@ -0,0 +1,111 @@
+package org.qortal.test.group;
+
+import static org.junit.Assert.*;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.qortal.account.PrivateKeyAccount;
+import org.qortal.data.transaction.CreateGroupTransactionData;
+import org.qortal.data.transaction.UpdateGroupTransactionData;
+import org.qortal.group.Group.ApprovalThreshold;
+import org.qortal.repository.DataException;
+import org.qortal.repository.Repository;
+import org.qortal.repository.RepositoryManager;
+import org.qortal.test.common.Common;
+import org.qortal.test.common.GroupUtils;
+import org.qortal.test.common.TestAccount;
+import org.qortal.test.common.transaction.TestTransaction;
+import org.qortal.transaction.CreateGroupTransaction;
+import org.qortal.transaction.Transaction;
+import org.qortal.transaction.Transaction.ValidationResult;
+import org.qortal.transaction.UpdateGroupTransaction;
+
+public class GroupBlockDelayTests extends Common {
+
+	@Before
+	public void beforeTest() throws DataException {
+		Common.useDefaultSettings();
+	}
+
+	@After
+	public void afterTest() throws DataException {
+		Common.orphanCheck();
+	}
+
+	@Test
+	public void testCreateGroupBlockDelayValues() throws DataException {
+		try (final Repository repository = RepositoryManager.getRepository()) {
+			TestAccount alice = Common.getTestAccount(repository, "alice");
+
+			// Check we're starting with something valid
+			Transaction transaction = buildCreateGroupWithDelays(repository, alice, 10, 40);
+			assertEquals(ValidationResult.OK, transaction.isValid());
+
+			transaction = buildCreateGroupWithDelays(repository, alice, -1, 40);
+			assertNotSame("Negative minimum block delay should be invalid", ValidationResult.OK, transaction.isValid());
+
+			transaction = buildCreateGroupWithDelays(repository, alice, 10, -1);
+			assertNotSame("Negative maximum block delay should be invalid", ValidationResult.OK, transaction.isValid());
+
+			transaction = buildCreateGroupWithDelays(repository, alice, 10, 0);
+			assertNotSame("Zero maximum block delay should be invalid", ValidationResult.OK, transaction.isValid());
+
+			transaction = buildCreateGroupWithDelays(repository, alice, 40, 10);
+			assertNotSame("Maximum block delay smaller than minimum block delay should be invalid", ValidationResult.OK, transaction.isValid());
+
+			transaction = buildCreateGroupWithDelays(repository, alice, 40, 40);
+			assertEquals("Maximum block delay same as minimum block delay should be OK", ValidationResult.OK, transaction.isValid());
+		}
+	}
+
+	private CreateGroupTransaction buildCreateGroupWithDelays(Repository repository, PrivateKeyAccount account, int minimumBlockDelay, int maximumBlockDelay) throws DataException {
+		String owner = account.getAddress();
+		String groupName = "test group";
+		String description = "random test group";
+		final boolean isOpen = false;
+		ApprovalThreshold approvalThreshold = ApprovalThreshold.PCT40;
+
+		CreateGroupTransactionData transactionData = new CreateGroupTransactionData(TestTransaction.generateBase(account), owner, groupName, description, isOpen, approvalThreshold, minimumBlockDelay, maximumBlockDelay);
+		return new CreateGroupTransaction(repository, transactionData);
+	}
+
+	@Test
+	public void testUpdateGroupBlockDelayValues() throws DataException {
+		try (final Repository repository = RepositoryManager.getRepository()) {
+			TestAccount alice = Common.getTestAccount(repository, "alice");
+
+			int groupId = GroupUtils.createGroup(repository, "alice", "test", true, ApprovalThreshold.ONE, 10, 40);
+
+			// Check we're starting with something valid
+			Transaction transaction = buildUpdateGroupWithDelays(repository, alice, groupId, 10, 40);
+			assertEquals(ValidationResult.OK, transaction.isValid());
+
+			transaction = buildUpdateGroupWithDelays(repository, alice, groupId, -1, 40);
+			assertNotSame("Negative minimum block delay should be invalid", ValidationResult.OK, transaction.isValid());
+
+			transaction = buildUpdateGroupWithDelays(repository, alice, groupId, 10, -1);
+			assertNotSame("Negative maximum block delay should be invalid", ValidationResult.OK, transaction.isValid());
+
+			transaction = buildUpdateGroupWithDelays(repository, alice, groupId, 10, 0);
+			assertNotSame("Zero maximum block delay should be invalid", ValidationResult.OK, transaction.isValid());
+
+			transaction = buildUpdateGroupWithDelays(repository, alice, groupId, 40, 10);
+			assertNotSame("Maximum block delay smaller than minimum block delay should be invalid", ValidationResult.OK, transaction.isValid());
+
+			transaction = buildUpdateGroupWithDelays(repository, alice, groupId, 40, 40);
+			assertEquals("Maximum block delay same as minimum block delay should be OK", ValidationResult.OK, transaction.isValid());
+		}
+	}
+
+	private UpdateGroupTransaction buildUpdateGroupWithDelays(Repository repository, PrivateKeyAccount account, int groupId, int newMinimumBlockDelay, int newMaximumBlockDelay) throws DataException {
+		String newOwner = account.getAddress();
+		String newDescription = "random test group";
+		final boolean newIsOpen = false;
+		ApprovalThreshold newApprovalThreshold = ApprovalThreshold.PCT40;
+
+		UpdateGroupTransactionData transactionData = new UpdateGroupTransactionData(TestTransaction.generateBase(account), groupId, newOwner, newDescription, newIsOpen, newApprovalThreshold, newMinimumBlockDelay, newMaximumBlockDelay);
+		return new UpdateGroupTransaction(repository, transactionData);
+	}
+
+}
diff --git a/src/test/resources/test-settings-v2.json b/src/test/resources/test-settings-v2.json
index 31fc2672..57eb22a5 100644
--- a/src/test/resources/test-settings-v2.json
+++ b/src/test/resources/test-settings-v2.json
@@ -2,5 +2,6 @@
   "restrictedApi": false,
   "blockchainConfig": "src/test/resources/test-chain-v2.json",
   "wipeUnconfirmedOnStart": false,
+  "testNtpOffset": 0,
   "minPeers": 0
 }