Any home brew project is susceptible to misunderstandings in how the time stamp is applied, and you need specialised timing equipment to unravel what is going on at frame and field level. For this reason i would not necessarily go down a DIY route. I would buy a VTI that is fully characterised. There are many, but the two in common use by occultation observers is the GPSBOXSPRITE2 by Blackboxcamera (london) and the IOTA VTI V3 by Videotimers (US). Both these derive the time from GPS and produce time stamps at field level. Ideal for our proposes.
I recently used a WAT-910 HX and recorded a Gemind lunar impact (30cm F/4). It had already been picked up by a 1 m scope but I was able to find the exact frame to 0.02s, and it was there (just). A good example of the importance of coordinated time.
Nick said that frame buffering can effect timeing. It does and a full description for various cameras in general use is published by G Dangl http://www.dangl.at/ausruest/vid_tim/vid_tim1.htm
The project described at ESOP36 (thank Alex) probably has been tested now, and verified, and similar components should work in the same way ( i guess) – best of luck with the project, and please report any occultations you time to the Lunar Section. They are very useful