Thanks everyone! This is amazingly helpful. The hour estimates are particularly good to have. I ran N1 last summer using the (then new) playtest rules in about 5 short weeknight (2.5 or 3-hour) sessions but had to cut a lot of the final dungeon. I easily could have made that last another 1-3 sessions, meaning that one could have used 20 hours of play, but my players did explore pretty much everything they could.
I was kinda wondering if T1-4 would need about 80 hours of play for the full experience or not, but it sounds like it could easily take 3 months of 3-hour weekly sessions and that might include some tricks that decrease play time a bit. Not sure if doing a 5th edition conversion would make it take less time or not yet.
I wish old school (and new old school) modules gave some approximation of play duration. Obviously it's super variable, but just knowing this might be a 40+ hour module lets me plan quite a bit more.