Ensure all online accounts timestamps are a multiple of the online timestamp modulus.

This is a simple way to discard the 5-minute online account timestamps (from out of date nodes) once the switch to 30-minute online account timestamps has taken place.

src/main/java/org/qortal/controller/OnlineAccountsManager.java

@@ -217,6 +217,11 @@ public class OnlineAccountsManager {
             return false;
         }
 
+        // Check timestamp is a multiple of online timestamp modulus
+        if (onlineAccountTimestamp % getOnlineTimestampModulus() != 0) {
+            return false;
+        }
+
         // Verify signature
         byte[] data = Longs.toByteArray(onlineAccountData.getTimestamp());
         boolean isSignatureValid = onlineAccountTimestamp >= BlockChain.getInstance().getAggregateSignatureTimestamp()