fix: TheadPoolTimer.CreatePeriodicTimer raises events properly

src/Uno.UI.RuntimeTests/Tests/Windows_System_Threading/Given_ThreadPoolTimer.cs

@@ -0,0 +1,40 @@
+using System;
+using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Windows.ApplicationModel.Core;
+using Windows.System;
+using Windows.System.Threading;
+using Windows.UI.Core;
+
+namespace Uno.UI.RuntimeTests.Tests.Windows_System
+{
+	[TestClass]
+	public class Given_ThreadPoolTimer
+	{
+		[TestMethod]
+		public async Task When_Timer()
+		{
+			var handlerCount = 0;
+			var timer = ThreadPoolTimer.CreateTimer(_ => handlerCount++, TimeSpan.FromMilliseconds(100));
+
+			await Task.Delay(500);
+
+			Assert.AreEqual(handlerCount, 1);
+
+			await Task.Delay(500);
+
+			Assert.AreEqual(handlerCount, 1);
+		}
+
+		[TestMethod]
+		public async Task When_PeriodicTimer()
+		{
+			var handlerCount = 0;
+			var timer = ThreadPoolTimer.CreatePeriodicTimer(_ => handlerCount++, TimeSpan.FromMilliseconds(100));
+
+			await Task.Delay(500);
+
+			Assert.IsTrue(handlerCount > 1);
+		}
+	}
+}

src/Uno.UWP/System.Threading/ThreadPoolTimer.cs

@@ -34,7 +34,7 @@ internal ThreadPoolTimer(TimerElapsedHandler handler, TimeSpan? period = null, T
 
 			_timer.Change(
 				period: period ?? global::System.Threading.Timeout.InfiniteTimeSpan,
-				dueTime: delay ?? global::System.Threading.Timeout.InfiniteTimeSpan
+				dueTime: delay ?? TimeSpan.Zero
 			);
 		}