They do not start immediately, but anything can happen. I usually see mine start about 45 minutes after lights out. Complete darkness is preferred. Tough for me since some of my breeders are in my TV room upstairs. In cases like that I cover the tank with giant beach towels so the TV doesn't interrupt the hatching.
Being that this is your first hatch I would simply keep the tank in darkness and check it every 30 minutes with a quick shine of a LED flashlight. The babies (if hatched) will be swimming around and noticeable. Sometimes with first time breeding parents the hatches can be "Not so precise", happening over a couple days, or more likely than not "..as soon as you think they aren't going to hatch and turn the pumps back on and go to bed" Next morning you realize you missed it :lol:
If you do not see anything after 4 hours, chances are it isn't going to happen, but not always. See above statement.
You'll get into a routine once you get yourself established to their pattern.
Have a Great Night Walt!