How to stop a while loop with long delay

Hi everyone,
I am building a simple program for turning on and off a single Bit.  The task is to turn ON the Bit for a period length T1, and OFF the Bit for a period length T2. T1 is normally different from T2, and can be controlled  by users. 
Since T1 and T2 can be variable, they sometimes can be very long.
If I use a Wait function inside a While loop, it needs long delay to be able to Stop the Main program.
The same situation happens when I use Timed loop.
Can anyone suggest me how to do this task?
Thanks a lot. 
Message Edited by tatuan on 04-12-2010 12:56 AM

Here's another possibility using OpenG Wait ms:
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