Based on my memory . . . will let a more recent grad correct what has changed . . .
Virtually all USNA grads attend some sort of school after graduation. Typically, you are assigned to a unit (ship/land) prior to attending school and your school date is selected as part of the service selection process. Pilots and submariners have the longest school track -- 1.5 to 2 years, if memory serves. SWO, USMC ground, SEALs, etc. have schools as well, but they aren't quite as long.
After school, you go to your ship, squadron or ground unit, usually for 2.5-3 yrs. During that time, you deploy ROUGHLY 6 months out of 18 for ships, subs, and ship-based squadrons. However, when you're "home" (in port), you're at sea a lot for workups, exercises, etc. So it's much more like 10-12 months at sea.
After your sea tour, you'll typically rotate to a shore tour. In MOST cases, you work a normal 10-hr day. Some shore billets are "easier" and some "harder" in terms of hours.