Quick B6 JS question -- I'm using them as a backup to get home tonight, should I list for their JS now or wait until I miss my primary commute home?

Not sure if they are Delta-esque and don't care if I don't show, or UPS-style where they'll hold a grudge if I don't show. If I make my primary flight I probably won't have time to cancel my listing before I have to turn my phone off since the connection is very tight. The flip side is I don't know if there is a latest time where I can try to list for the B6 JS -- by the time I miss my primary commute I'll be within a couple hours of the B6 departure time.

Thanks!