Originally Posted by
worldwidetraveler
My itinerary starts with a United partner airline which connects to a United TATL flight. Can I check in on-line at united.com 24 hours before the first flight? ...
As others have mentioned the answer is no (initially). You must first check-in with the partner.
However, sometimes this does not fully check you in (such as get you on the gate upgrade list or get you a BP or you want to do SDC), if that happens you will be able to check-in with UA
once the partner puts the ticket coupon for their flight. This probably will not be until after your board the partner's flight. So if there is inflight wifi or on landing you can finish the check-in with UA.