Engine cleaning shouldn't take no more than 15mins tops!
1. Start engine and warm up.
2. Spray degreaser liberally (Not WD-40)
3. Let degreaser work ~2 mins
4. Agitate heavily soiled areas with brush
5. Power wash (~1500psi and less. Much safer IMO from 1 meter away than 'flooding' with hose. Water out of PW is comprised of a lot of air)
6. Close hood (evaporate the majority of water), and continue with the rest of detail (Exterior/interior)
7. When done everything else, open the hood, and wipe up remaining isolated puddles of water.
8. Spray dressing, and wipedown.
**Disclaimer**
There are probably a million ways to wash your engine-- and the technique will differ from person to person.
To be honest, unless your car is 20 years old, you'll be safe with the pressure from the hosehold hose. New engine compartments are built to withstand water, just as long as it isn't pressure washed (I do it, but you gotta be careful, keep a good distance) and concentrate the stream too long on one place, you should be fine. Obviously, take extra care around the fuses/battery/starter/alternator. Make sure the engine is warm before you start. Once you're finished, close the hood, and come back later to wipe up stray puddles of water. That easy.
Here's a video clip that may help:
http://www.adamspolishes.com/videos/cleaning_motor.cfm
Good luck
--Gabe