They use metric time. Divides evenly by 5.How does that split up over 24 hours, assuming the Enterprise works to Earth time? I know that DS9 operates over a 26 hour day based on Bajor's rotation, but that makes it more confusing.
Four shift rota I can understand. Even six, or three shift rota. But five? You work 4 hours 48 minutes a day?

Maybe most of it is actually spent in meditation? I don't know about you, but I don't always spend my "meal breaks" eating if there are errands to run or I need a nap instead. Being around emotional beings all the time might cause Spock to need to freshen up his control a bit here and there.- And his breakfast looks like it's from 06:00 to 07:30! Whatever is he eating to warrant such long breaks?