Wirelessly posted (BlackBerry9650/5.0.0.975 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/105)
I'm on BOS-BWI.
Edit to add: Well, just for giggles, I decide to call again this morning to see what B6 would say. This agent confidently told me that I could check-in my bag 4 hours before the standby flight and confirmed that my bag would be tagged as a standby bag and removed from the aircraft if I didn't clear the standby list.
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Another edit to add: So I showed up 4 hrs before the standby flight. Got my standby card and checked luggage tagged as standby. Easy-peasy lemon squeasy.
The process is very similar to other airlines - good to know.