diff --git a/src/Aeon.Acquisition/CreateGroup.cs b/src/Aeon.Acquisition/CreateGroup.cs
new file mode 100644
index 0000000..fe0d1f3
--- /dev/null
+++ b/src/Aeon.Acquisition/CreateGroup.cs
@@ -0,0 +1,108 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Reactive.Linq;
+using Bonsai;
+using Bonsai.Expressions;
+
+namespace Aeon.Acquisition
+{
+    [Description("Creates a sequence of grouped observables for each key in the input sequence.")]
+    public class CreateGroup : WorkflowExpressionBuilder
+    {
+        static readonly Range<int> argumentRange = Range.Create(lowerBound: 1, upperBound: 1);
+
+        public CreateGroup()
+            : this(new ExpressionBuilderGraph())
+        {
+        }
+
+        public CreateGroup(ExpressionBuilderGraph workflow)
+            : base(workflow)
+        {
+        }
+
+        public override Range<int> ArgumentRange => argumentRange;
+
+        public override Expression Build(IEnumerable<Expression> arguments)
+        {
+            var source = arguments.FirstOrDefault();
+            if (source == null)
+            {
+                throw new InvalidOperationException("There must be at least one input to the create group operator.");
+            }
+
+            Type keyType, elementType;
+            var sourceType = source.Type.GetGenericArguments()[0];
+            var selectorParameter = Expression.Parameter(source.Type);
+            if (sourceType.IsGenericType && sourceType.GetGenericTypeDefinition() == typeof(IGroupedObservable<,>))
+            {
+                var sourceTypeArguments = sourceType.GetGenericArguments();
+                keyType = sourceTypeArguments[0];
+                elementType = sourceTypeArguments[1];
+            }
+            else
+            {
+                keyType = sourceType;
+                elementType = null;
+            }
+
+            return BuildWorkflow(new[] { selectorParameter }, null, selectorBody =>
+            {
+                var selector = Expression.Lambda(selectorBody, selectorParameter);
+                var resultType = selectorBody.Type.GetGenericArguments()[0];
+
+                return Expression.Call(
+                    typeof(CreateGroup),
+                    nameof(Process),
+                    elementType != null
+                        ? new[] { keyType, elementType, resultType }
+                        : new[] { keyType, resultType },
+                    source, selector);
+            });
+        }
+
+        static IObservable<IGroupedObservable<TKey, TResult>> Process<TKey, TResult>(
+            IObservable<TKey> source,
+            Func<IObservable<TKey>, IObservable<TResult>> selector)
+        {
+            return source.Select(key => new GroupedObservable<TKey, TResult>(
+                key,
+                selector(Observable.Return(key))));
+        }
+
+        static IObservable<IGroupedObservable<TKey, TResult>> Process<TKey, TSource, TResult>(
+            IObservable<IGroupedObservable<TKey, TSource>> source,
+            Func<IObservable<IGroupedObservable<TKey, TSource>>, IObservable<TResult>> selector)
+        {
+            return source.Select(group => new GroupedObservable<TKey, TResult>(
+                group.Key,
+                selector(Observable.Return(group))));
+        }
+
+        class GroupedObservable<TKey, TElement> : IGroupedObservable<TKey, TElement>
+        {
+            public GroupedObservable(TKey key, IObservable<TElement> source)
+            {
+                if (source is null)
+                {
+                    throw new ArgumentNullException(nameof(source));
+                }
+
+                Key = key;
+                Source = source.Publish().RefCount();
+            }
+
+            public TKey Key { get; }
+
+            private IObservable<TElement> Source { get; }
+
+            public IDisposable Subscribe(IObserver<TElement> observer)
+            {
+                return Source.Subscribe(observer);
+            }
+        }
+    }
+}
diff --git a/src/Aeon.Acquisition/SynchronizerMonitor.bonsai b/src/Aeon.Acquisition/SynchronizerMonitor.bonsai
index c6ad44b..2cf2145 100644
--- a/src/Aeon.Acquisition/SynchronizerMonitor.bonsai
+++ b/src/Aeon.Acquisition/SynchronizerMonitor.bonsai
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<WorkflowBuilder Version="2.8.1"
+<WorkflowBuilder Version="2.8.2"
                  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                  xmlns:rx="clr-namespace:Bonsai.Reactive;assembly=Bonsai.Core"
                  xmlns:harp="clr-namespace:Bonsai.Harp;assembly=Bonsai.Harp"
@@ -91,13 +91,20 @@
       <Expression xsi:type="MemberSelector">
         <Selector>Item2</Selector>
       </Expression>
+      <Expression xsi:type="harp:Parse">
+        <harp:Register xsi:type="harp:ParseMessagePayload">
+          <harp:PayloadType>Timestamp</harp:PayloadType>
+          <harp:IsArray>false</harp:IsArray>
+        </harp:Register>
+      </Expression>
       <Expression xsi:type="Combinator">
         <Combinator xsi:type="rx:Zip" />
       </Expression>
       <Expression xsi:type="scr:ExpressionTransform">
         <scr:Expression>new(
 Item1 as Stats,
-Item2 as Names)</scr:Expression>
+Item2 as Names,
+Item3 as SyncTimestamp)</scr:Expression>
       </Expression>
       <Expression xsi:type="SubscribeSubject">
         <Name>HeartbeatSources</Name>
@@ -111,7 +118,7 @@ Item2 as Names)</scr:Expression>
       <Expression xsi:type="scr:ExpressionTransform">
         <scr:Expression>new(
 Item1.Stats.Mean as MeanTimestamp,
-DateTime(1904, 1, 1) + TimeSpan.FromSeconds(Item1.Stats.Mean) as MeanUtcTimestamp,
+DateTime(1904, 1, 1) + TimeSpan.FromSeconds(Double.IsNan(Item1.Stats.Mean) ? Item1.SyncTimestamp : Item1.Stats.Mean) as MeanUtcTimestamp,
 Item2 as ExpectedDeviceCount,
 Item1.Stats.Count as DeviceCount,
 Item1.Stats.Maximum - Item1.Stats.Minimum as MaxDifference,
@@ -128,18 +135,20 @@ string.Join("\t", Item1.Names) as Elements)</scr:Expression>
       <Edge From="5" To="8" Label="Source1" />
       <Edge From="6" To="7" Label="Source1" />
       <Edge From="7" To="8" Label="Source2" />
+      <Edge From="7" To="13" Label="Source1" />
       <Edge From="8" To="9" Label="Source1" />
       <Edge From="9" To="10" Label="Source1" />
       <Edge From="9" To="12" Label="Source1" />
       <Edge From="10" To="11" Label="Source1" />
-      <Edge From="11" To="13" Label="Source1" />
-      <Edge From="12" To="13" Label="Source2" />
-      <Edge From="13" To="14" Label="Source1" />
-      <Edge From="14" To="17" Label="Source1" />
-      <Edge From="15" To="16" Label="Source1" />
-      <Edge From="16" To="17" Label="Source2" />
-      <Edge From="17" To="18" Label="Source1" />
+      <Edge From="11" To="14" Label="Source1" />
+      <Edge From="12" To="14" Label="Source2" />
+      <Edge From="13" To="14" Label="Source3" />
+      <Edge From="14" To="15" Label="Source1" />
+      <Edge From="15" To="18" Label="Source1" />
+      <Edge From="16" To="17" Label="Source1" />
+      <Edge From="17" To="18" Label="Source2" />
       <Edge From="18" To="19" Label="Source1" />
+      <Edge From="19" To="20" Label="Source1" />
     </Edges>
   </Workflow>
 </WorkflowBuilder>
\ No newline at end of file