There are Challenge achievements for speed running Acts 1-5 in one hour each. Do I need to start a new character in order to do that? Is it enough to go into Campaign mode and go through the quests of a given act in one session?
If you are referring to the Sprinter Conquest, that is running Acts 1-5 in Campaign under 1 hour Total, not Acts 1-5 in 1 hour each.
The timer starts when you enter the Game and ends when you kill Malthael.
It can be done on Normal difficulty.
You need to start a game with a level 70 character on any difficulty level (Normal is typical) and the clock starts once you enter the game. You need to complete the entire campaign from the first quest in Act 1 to the last quest in Act 5 within 1 hour. You generally do it in a group and usually have 1 party member stay in town to complete all the NPC interactions the moment the other party members complete the various quest actions once they are completed.
You need to gear for speed and more speed and utilize your classes mobility skills if they have them (Dashing Strike, Steed Charge, Spirit Walk, etc.) since at normal difficulty you can clear screens by just running past enemies.
I mean those basic non-season achievements where you have one hour per act. It seems that it’s possible to do all acts in an hour. Can I speed run later acts by going through all their quests in another session? I mean, I would like to split my speed runs into 5 games, one for each act. I would like to avoid doing all acts at once.
Yes, those achievements are for each individual act, standalone, and no you don’t need a new character, you can use an existing one. I got the Act 4 in an hour achievement a couple of months ago by accident, while just messing around.
Just be sure it’s a fresh session, pick your act in campaign mode, and charge. It’s not much of a challenge, but ideally you’ve tuned your build to be at least a little fast, and that should be all it takes.