Hey bvkerbear,

Olive oil, especially extra virgin olive oil (EVOO) is really heavy. I'd recommend it for overnight treatments only.

Whenever I know that I'll be washing all of my hair in the morning, I try to do a heavy EVOO treatment the night before. I first divide my hair in half and comb each side. Then I pour a little olive oil in the palm of my hand, rub my palms together and then slick them down the length of one side of my hair. I concentrate most of the oil on the ends. Then I do the same with the other side. When that's done, I'll usually pour a little more oil into my hand, rub my palms together and do my entire hair like that, bringing the 2 sections together for a "collective" oiling. If it's just for overnight, you can really load it on and not worry about being too greasy - you're supposed to be.
    Anyway, then I twist my hair into a kind of loose bun and balance it on the back of my head while slipping on my sleep cap. You can find these at Wal*Mart for dirt cheap. Satin slumber caps, I think they're called. They're a little tricky to get used to at first, and I suppose you could also use a shower cap - I just could't sleep with all of that plastic crunching around my head. lol
    So I leave it like that until the next morning when I pull off the sleep cap, carefully comb out my greasy locks and wash them as usual. There is no trace of olive oil left over after washing - just smooth hair. 

Anyway, hope that answered your q's.