I am scheduled to fly PHL-SFO on Sunday 11-16. I just got off the phone with a CP rep. and she told me that my fare was "time specific" (5:30 pm) and oculd only fly stand by from 5:50 pm through 5:50 am the next day. Otherwise i neded to pay the $100 change fee, and the differencein fares.
She also said that at htis point (Wednesday) there isplenty of availability on the two mornng flights.
She sais US will not allow a stand by for a CP with this fare even when there are empty seats available? Is this right? I don't get it.

PS I did a search for this topic and couldn't find anything.

That's a new one on me.

Try calling again?

There are time specific fares (i.e. no later than 5pm on Sundays) for the Shuttle but you're not flying the Shutttle.

I've hit this once also - "time specific fare" and different calls to cp desk yielded the same answer.

Perhaps the ticket counter or gate agent could override but in my case I didn't want to get to the airport so so early and then not have it work.

Not sure what fare code or fare basis causes this