How does the time/calendar work?

[slasktratten]

Could someone explain how timekeeping works in this game?

E.g. before rest at the stronghold, the watch says:

Day 16, Hour 14, 14 Fonprima, 2823 AI

 

then after 8 hours of rest:

Day 17, Hour 22, 14 Fonprima, 2823 AI

 

Shouldn't it still be day 16, or does the day not start on hour 0?