Hotels use various strategies to manage bed availability until rooms can be cleaned for the next guest.
Charging anyone a fee for "early" check-in is kind of a shakedown, IMO.
How would they like for EVERY guest checking in that day to arrive at 3PM?
Talk about long lines.
I've never been turned away when checking in "early", even 10 am.
Might be told room isn't ready yet, had to park bags at bell desk, but was "checked-in."