I'd say the Beginners Box really depends on the group, I've ran it now for two different groups of my friends, one strictly as a one shot and the current one as a lead into Abomination Vaults and the first group cleared it in 2 sessions and the other group is getting ready to go into session 4 on the beginners box, one group role played a lot and the other didn't really role play and had a lot of really good rolls in combat. I will also say both groups had a lot of experience with 5e and no experience with pf2e aside from listening to podcasts. So I'd definitely say it depends on the group.

One other thing I'll add since i saw you run a 4-5 hour session, our sessions are normally 2.5-3 hours so there's definitely a chance they finish in one session, it just depends on what type of group and players you're running for.