My longest match ever was in my junior tournament days. Started at 10AM and ended around 6PM because of two rain delays. It started raining a few games into the first set, so they pulled all matches and told us to wait it out, then they dried the courts, and put us back on with a 10 min warmup. We got a few more games in before it started raining again, and this time it didn't look like it was going to let up so they had to move all the outdoor matches from a few different sites over to a nearby indoor club. At least the second time we knew we wouldn't go on for a while and they said come back at 3. Of course putting that many matches on with that many fewer courts they fell behind schedule and we didn't go back until about 4:30. I ended up losing, but if I had kept winning I would have had to play my next round at night, then the semi's were pushed to Sunday morning and the finals would be played later that afternoon. That would have been tough.
As far as actual playing time, I can't think of any remarkably long matches, and got used to playing pretty quick matches. I remember in college our matches didn't last very long because most of the time you just took turns holding serve with quick points until someone got a few key returns in to snag a break.