Online checkin doesn’t accomplish anything more than getting your CC linked to your resort account, setting PINs for everyone who can charge to the room, and submitting room location requests (if the options work for you) so that you can skip the front desk and go straight to your room when you arrive. (But you can still go to the desk when you arrive, if you want to.) So you can finish the online checkin anytime you want - or even skip it and just check in at the desk in person.