If only things were that simple.
You set out from IronForge this morning at about 8. It was a half a day's journey to the Durzh's tower, so you arrived there around midday. Since then you've clambered over the pittrap, fought off some were-rats, gone upstairs and had a bit of a look around and had everything up there burnt to a crisp, gone downstairs and had a look around, fought and killed an earth-elemental, and now had a look around the storage area. All this I think would have taken you maybe 2 hours. So it's about 2pm. You can rest up for 10 hours with 4 watches of 2.5 hours each and you'll basically have had your 8 hours sleep each to regain spells etc. This will take you through to midnight. If Namfoodle prays at dawn he will not have his spells back though. Namfoodle what time of day do you pray?
I'm randomly deciding that watches will be in alphabetical order (Amaryllis, Namfoodle, Seebor, Tomas), which has the advantage of putting Namfoodle at sunset if that's when he prays.
Not that any of this matters because .... (blame the die not the DM!) Amaryllis wearily sits through her watch tired although it is only mid-afternoon from the excitement of the day when she suddenly hears the footsteps of what seems like 2 people coming up the stairs.