Here's some UA language I needed to research. My read on 'missed trip provisions' is that you've got up to 2 hours for a standby to be legit with no add/collect or fees. Good luck let us know your experience!


<snip from somewhere else>
STANDBYS

APPLIES FOR U.S. 50 STATES / SJU/STT / CANADA
(INTERNATIONAL: STANDBY NOT PERMITTED)

THIS INCLUDES UA-DESIGNATED CODE SHARE


-STANDBY IS ALLOWED FOR AN EARLIER/LATER SAME DAY FLIGHT FOR PASSENGERS HOLDING CONFIRMED RESERVATIONS AND TICKETS WITHOUT ADD-COLLECT/SERVICE CHARGE.
-STANDBY FOR ALTERNATE SAME-DAY FLIGHT(S) IS PERMITTED FOR ANY FLIGHT - PASSENGER IS NOT LIMITED TO FLIGHT(S) LISTED IN THE FLIGHT-SPECIFIC RESTRICTION AS LONG AS ORIGIN AND DESTINATION AIRPORTS REMAIN THE SAME.
-CUSTOMERS MAY BE PUT ON THE AIRPORT STANDBY LISTING ONLY WITHIN FOUR HOURS OF THEIR DESIRED FLIGHT TIME. (NOTE: STANDBY IS PERMITTED FOR GROUNDLINK SERVICES)
STANDBY:

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PASSENGERS HOLDING CONFIRMED RESERVATIONS AND TICKETS MAY STANDBY FOR AN EARLIER/LATER SAME DAY FLIGHT.

MISSED TRIP PROVISIONS:
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(FOR INTERNATIONAL GUIDELINES SEE: %S*FAR/RULE 80.)
A PASSENGER PRESENTING HIMSELF/HERSELF AT THE AIRPORT OF DEPARTURE NOT LATER THAN 2 HOURS AFTER THE SCHEDULED DEPARTURE TIME OF THE FLIGHT SHOWN ON THE PASSENGERS TICKET MAY STAND BY FOR THE NEXT FLIGHT OF THE SAME CARRIER...EVEN IF THE NEXT MORNING.
ANY SERVICE CHARGE WILL BE WAIVED...AND NO ADD COLLECT FOR AN INCREASE IN FARE WILL BE MADE.