I often get an EUA after the 24 hour window, but if you check in online, you are no longer eligible for an EUA. Also a lot of times I get the EUA when I start the OLCI process, but don't finish it. Basically standard procedure for me is to attempt OLCI at the 24 hour mark, then again before I go to sleep the night before the flight, and again when I wake up. A lot of times when I wake up I am already EUAed, or it goes through when I try OLCI. I don't know if this reduces my chances of a battlefield upgrade, but I have been quite successful with that method so I stick to it.