A DVD will (nearly always fit on a DVD, so that is not the problem. However, because of the MPEG2 encoding, youmight loose quality when you try to make a DVD with too much video-time. Assuming you like to havethe highest quality, the maximum time is a littlebit more then 1 hour on a 4.3Gb DVD. The exact figures depend on a number of things like the menu, audio, data files, the amount of movement in your video (thats because of he way the MPEG2 encoder work) etc. Lowering the bitrate will allow you to add more minutes to the DVD, but decreases the quality. It is up to you to decide what you find acceptable.
For me, I always try to keep the time below 70 minutes. In fact, I like to make short videos more then long video’s…
Theo