Originally Posted by
mahasamatman
I do not believe that is correct. Nowhere does UA specify in what time zone the hold ends - most reports place it as Eastern Time regardless of where the flight originates.
Originally Posted by
petal
I suppose I didn't want to see it

, but was (incorrectly) advised by the MP agent that the HOLD was based on the time zone of the departure city. I got lucky!
The hold always ends at 11:59 Eastern Time, but the hold DOES depend on the time zone of the departure city in a way.
Right now it is 12:45AM CDT 4/28. If I put a ORD-BOS flight on hold, that hold will expire on 4/29. However, if I put a SFO-BOS flight on hold right now, that hold will expire on 4/28, as it is 10:45PM, 4/27, in SFO right now.
The hold expires the next day from the reference point of the departure city, even as the expiration time will always be 11:59 Eastern Time.