If you use the usual timer component in Delphi (which is really just the standard Windows timer) don't expect to get accurate timing - it is affected by screen redraws etc (try grabbing a window and moving it - the timing will go out the window) since it is based on the application message pump. There is a multimedia timer that involves a bit of work to get going that has much better resolution and repeatability. So best not to rely on Windows for accurate timing! The idea of sending stop/start commands and having the 8051 do the timing is a reasonable solution.

I too have used the apdpro stuff and find it good.