You have both of those days to weigh in. So if you wake up on the 11th and are making your weight, then submit it. If you wake up on the 12th and make weight, you can weigh in then.
Final Weigh-Ins (Or "Weigh-Out"). A final weigh-in may be completed the day after a dietbet ends, starting at 12:01 AM, PT. The window to submit a final weigh-in is 48 hours. At the end of the 48-hour window, weigh-ins can no longer be submitted and you cannot qualify to win. If your final weigh-in isn’t approved by our Referees, you will have 12 hours to re-submit your weigh-in with a new set of photos. If you miss this deadline or your resubmitted weigh-in is rejected within 12 hours afterward, then you may not be eligible to win the game. While we're happy to give you one more chance to resubmit your weigh-in, we also need to be considerate of all the other players waiting for this game to finalize and collect their winnings.