You can easily spend 5 active days in Athens, even without visiting any archaeological sites.
See on the official Athens website:
https://www.thisisathens.org/
It is possible to visit the Acropolis and the Acropolis Museum in the same day.
If you want to avoid possible long queues at the ticket office the visit to the Acropolis must be planned in advance by reserving a date and a time slot and be at the entrance to the site 15 minutes before.
Buy your tickets here:
https://hhticket.gr/tap_b2c_new/english/tap.exe?PM=P1N
Tickets for the Acropolis Museum can be purchased here:
https://www.theacropolismuseum.gr/en/