From Xojo Documentation
Creates a client-side (browser) timer that executes code based on the time set. This control has no visual user interface but it appears on the Shelf in the Web Page Layout Editor.
The WebTimer is very similar to the desktop Timer control. The important difference is that the WebTimer is part of the page. As a result, it is controlled from the page, which is on the client side.
A WebTimer can be used to update controls on the page, for example. A regular Timer control will only execute server-side, so it cannot contact the client. If you need to update a control on a page from a regular Timer, consider using the UpdateBrowser method.
The WebTimer provides the same functionality as the Desktop Timer control. This example updates the value on a label (SecondsPassedLabel) on the web page using the WebTimer. This code in the WebTimer updates the label:
You can also add a button to start and stop the timer. This code is in the WebButton.Pressed event:
Timer1.RunMode = WebTimer.RunModes.Multiple
Me.Caption = "Stop" // button caption
SecondsPassedLabel.Value = "0"
Timer1.RunMode = WebTimer.RunModes.Off // Turn off the timer
Me.Caption = "Start"