how long does it take to start mapping from scratch?

how many hours does it take?

Depends on your knowledge and experience. I have 1k hrs clocked on this game and it took 15 hrs more or less for me this league. I skipped all rituals until Blood Aqueducts. Would have been faster if I went slayer but instead I am elementalist melee ele hit. My passive tree starts from north pole (golem buffs) to Acrobatics on the far east, to Tribal Fury on the southwest tip. ;)

Just chill and enjoy the flow so you dont feel stressed.

For me ~9 hours, usually I'm in maps 2nd day of league, with all skill points and first 3 labs.

I skip league mechanics until reaching maps.

As the guys have said, it depends totally on your experience and how you play. World-class racers do it in about 2 hours.

I never timed it, but I'm always doing a new character each league, so I go slow and figure things out.

For a new player getting no help from friends, I would not be surprised if it took 40 hours.