Per session? Per campaign? Oh RPGaDay, you imprecisely worded list of specific questions, don't ever change. Ya'know what do, 'cause that would be really helpful.
These days, my sessions are all online and last about 4 hours or so, 5 if we push it. This is practical and sensible, since we often start in the evening and some of us have to get up early the next morning for work (myself included).
In my heyday and even up to few years back (pre-Pandemic), sessions averaged between 6 and 8 hours, with some going even longer. Obviously as folks get older and have families, commitments, and the inability to stay focused for long periods of time, shorter sessions are inevitable.
As for campaigns...
This is no set length for a campaign and length and quality are no indication of each other. Our Hogwarts and Star Trek campaigns (run by my friend Alex and I respectively) are each well into their 6th year, while my Sunday group tends to run a game for around a dozen or two dozen sessions before changing to something else. We will sometimes - though rarely - revisit a previous game, which is something I hope and intend to do with our Champions and Red Dwarf games.
Right now...well I won't go into it here. Be on the look out for a post that goes into my feelings on my games and campaigns at present in more detail tomorrow. For now, I think I've sufficiently answered the question.