When you say respawning, do you mean -host? My only problem with that is the maps don't reset when you die and there's no time at all displayed on the intermission screen (in 2.4.1 anyway).
The way prboom-plus does it, it remembers your total time when you enter a level. If you enter map02 at 30 seconds and you die in map02 at 45 seconds, the time will go back to 30 seconds when you restart map02 (whereas in ZDoom the total time resets completely to zero). But, the prboom-plus way doesn't add the time from incomplete attempts (like I wrote about in my first post), it only keeps track of completed attempts.
If that total timer won't work, is there a way to see how many seconds or tics an lmp file is without re-watching it and writing down all the times by hand?