There are x frames per second in any movie, and I assume that's what FPS means in this
context. If you know the number of frames then it's simple math to decide duration.
But if you talk serious timecode math and/or having a live timeode display in excel, it
can't be done without serious macro programming and user defined functions. To the extent
that "why is Excel involved in this at all?".
An advanced www.google.com groups search for "timecode" in the excel groups will provide
some solutions and suggestions for timecode math (and a few postings similar to this as
well