What's the problem using the GetDate() function instead of GetTickCount()? The problem you are going to have is that if GetTickCount() is using the native Windows GetTickCount() call (which I think it does), the tick count is a 32 bit word value that starts at zero when the computer is booted. Also, it has limited range that rolls over at about 26 days.
If you only need resolution down to the second, I would rethink the solution using the GetDate() value.