How long does it take to fill a water heater and for the water to heat up?

I had to get a new one yesterday, when I came back home from holiday I noticed that there were water dripping from my water heater So the janitor told me I had to get a new one, and I had a plumber over yesterday to fix it.
It only occurred to me early this morning to actually fill it up (honestly, the plumber should have known I'd be silly with household things and do it for me). But now, 7 hours after, the water is still cold.

So.. is it time for me to call the janitor again (it's saturday evening, is it ok to call him now anyways?) or is this perfectly normal?


*feels silly and blond, and think that every apartment should come with its own handy-man to fix these things*