There are a few different answers, depending on your situation:
1) If you bought the tickets separately from your hotel reservation, then yes. You can go directly to the parks before you check in. And as long as the tickets and your hotel are linked to the same MDE profiles, you can use your MagicBands to access those tickets for park entry, even before going to the hotel.
2) If you bought tickets as part of a package reservation, and you used the *direct-to-room* feature of online checkin, then yes, you can go to the parks before checkin. Doing direct-to-room should activate all aspects of your package as-of the time you enter as your arrival time. (So put something early, like 7am or 8am)
3) If you use any other function to check in other than direct-to-room, you will most likely have to go to the hotel first before you can use the ticket.
(and these are all as it stands now... There was one post recently on here that said a CM told them all tickets may be activated automatically day-of-checkin)
-Rob