Forms

The default value of this property is zero (0). This means that code is not executed in the OnTimer trigger.

You can specify a TimerInterval value in milliseconds ranging from zero to the highest defined integer, which corresponds to approximately 25 days.

When you open a form for which you have specified a TimerInterval value, the OnOpenForm Trigger is executed. A timer then starts to count the TimerInterval in milliseconds. After the specified interval has elapsed, the OnTimer Trigger is executed. The timer then resets to zero and the process is repeated until the form is closed.

In some cases, the TimerInterval value specified may be too short to allow for complete execution of the OnTimer trigger before starting the next instance of the trigger. In this case, the number of overlapping instances is noted and the trigger is executed continuously for as long as necessary.

Problems with your computer's operating system can affect the performance of the timer.

Reference