For three days they're on offer to you and you alone. I can't use them or sell them to anyone else or, indeed, retract the offer. And this are 3 "real life" days, not game days. So don't worry, you have plenty of time to get the money.
Private offers also appear on the same page as public ones, but only for the intended airline. That's why you're seeing "your" Starliners among the other planes for sale.
