Decrease the block time threshold (3x)

neo.UnitTests/Consensus/UT_Consensus.cs

@@ -20,7 +20,6 @@
 
 namespace Neo.UnitTests.Consensus
 {
-
     [TestClass]
     public class ConsensusTests : TestKit
     {
@@ -36,6 +35,13 @@ public void Cleanup()
             Shutdown();
         }
 
+        [TestMethod, NotReRunnable]
+        public void TestPrepareRequestThreshold()
+        {
+            var service = new ConsensusService(null, null, null);
+            Assert.AreEqual(8 * Blockchain.TimePerBlock.TotalMilliseconds, service.PrepareRequestThreshold.TotalMilliseconds);
+        }
+
         [TestMethod]
         public void ConsensusService_Primary_Sends_PrepareRequest_After_OnStart()
         {

neo/Consensus/ConsensusService.cs

@@ -29,6 +29,7 @@ internal class Timer { public uint Height; public byte ViewNumber; }
         private ICancelable timer_token;
         private DateTime block_received_time;
         private bool started = false;
+        public readonly TimeSpan PrepareRequestThreshold = TimeSpan.FromMilliseconds(8 * Blockchain.TimePerBlock.TotalMilliseconds);
 
         /// <summary>
         /// This will record the information from last scheduled timer
@@ -405,7 +406,7 @@ private void OnPrepareRequestReceived(ConsensusPayload payload, PrepareRequest m
             if (context.RequestSentOrReceived || context.NotAcceptingPayloadsDueToViewChanging) return;
             if (payload.ValidatorIndex != context.Block.ConsensusData.PrimaryIndex || message.ViewNumber != context.ViewNumber) return;
             Log($"{nameof(OnPrepareRequestReceived)}: height={payload.BlockIndex} view={message.ViewNumber} index={payload.ValidatorIndex} tx={message.TransactionHashes.Length}");
-            if (message.Timestamp <= context.PrevHeader.Timestamp || message.Timestamp > TimeProvider.Current.UtcNow.AddMinutes(10).ToTimestampMS())
+            if (message.Timestamp <= context.PrevHeader.Timestamp || message.Timestamp > TimeProvider.Current.UtcNow.Add(PrepareRequestThreshold).ToTimestampMS())
             {
                 Log($"Timestamp incorrect: {message.Timestamp}", LogLevel.Warning);
                 return;