Maybe they can. Or maybe the party, through their own choices/mistakes (or simple bad luck), no longer has time for that, or already burned through whatever providence they were given. (As a reminder, Catnap only works 1/LR no matter how many times it is cast.)
Overriding that and fudging the clock is always a possibility. But DMs who choose to let the dice fall where they may are not wrong either, so long as everyone - the DM included - is having fun.