How long can a cake iced with stabilized whipped cream sit out? Also..can you put fondant accents on it like you would with buttercream?
Yes you can add fondant decorations but I don't know how long it can be left out.
I wouldn't put fondant on whipped cream, the moisture from it will wilt the fondant.
According to ServSafe, something that requires refrigeration is safe out at room temp for up to a 4 hour block of time, at the end of which any left-overs must be discarded.