Originally Posted by
Kmxu
During my mileage run days, I got to airports too early and had to wait for checkin counter to open, for example, HGH-HKG on CX, PVG-EWR/ORD/SFO on United. I needed a hard-copy boarding pass to go through immigration in those airports.
United website lists the minimum time for checkin for different airports. But OP was looking for the maximum time.
Ah yes, maybe my response was ambiguous. I agree that 3 hours is the safest assumption for maximum time. In my experience around the world, airlines will not staff counters more than 3h before a flight. Sometimes they will even refuse to check you in until 3h before the flight, even if they are staffed for another flight, such as NH in BKK.
For UA in EZE, I would not expect check-in to be available before 7p, since 10:05p EZE-IAH is the only UA flight. Sometimes self-print or mobile BP is acceptable if a BP is the only concern.