I'm at the 60 day mark today at 9:26 am EST but a choice for Online Checkin is not showing on my MDE Account. Is it precisely 60 days beginning at 3pm?
Never mind. I found it. You have to click "Reservations" > "Reservation Details" and in the top right of the pop-up box is "Check in Online". At 60 days that should be a prominent "Notification" link as soon as you log in.
