Originally Posted by
Kmxu
If you go to airport earlier, you can standby for any flight if there is a seat available. The gate agent will try to put you on a flight with seat on the second segment. Once you get to ORD, you can try to standby for an earlier ORD-EWR flight. Good luck.
This isn't true, assuming OP is on an OMA-EWR nonstop. You can't change routing on standby. (UA doesn't want you to get to ORD and then have no confirmed ticket to EWR).
OP: The "bucket leveling" thing basically doesn't happen for connecting flights. You need inventory all the way from OMA to EWR before you can make the change without paying a nasty fare difference -- and by the time you got to two hours before departure for ORD-EWR, you'd already have missed OMA-ORD.