There isn't an easy answer to your question because while it's fairly easy to do, there are a ton of variables that change the answer to your question. Total time is going to be:
Capture time + Render Time (if any) + Mastering time
Capture time will be how long it takes you to convert the analog sounds and images on the tape to a digital file on your PC. Render time will be the time it takes to convert your captured movie file into a format suitable to be mastered onto the DVD. If your PC is fast enough, you might be able to capture directly to a file format that can be converted to DVD. Mastering time is the time to setup and create the actual DVD.
Capturing, by it's nature has to be realtime or better. Your PC's performance will determine how fast the other stages can proceed. I've rendered 5 minutes of video on a Pentium and had it run all night. On a P4 I've captured and rendered simultaneously, in realtime. The quality at which you capture the video will also factor in. That probably does'nt answer your question directly, but it should give you an idea of what's involved.
