Timer Gurus - How to make a stable 30 second timer?

[dwacker]

Here's my problem: I need to generate an event every 30 seconds, but I need the event to occur at the same time consistently (+- 1 second) - with respect to the system clock.

I've written a simple app that starts a 30 second timer at 15 seconds into a minute interval. Unfortunately, I have observed that it does not stay synchronized to this start time ... so how can I reliably generate an event every 15 seconds and 45 seconds into each minute ... for an entire day?

All suggestions are welcome!

Dave