Yes, you can use olive oil easily, as well as the butter. Also, the tempertaure of the mixture does matter. If it gets too hot, the thc gets burned up and it renders the mixture useless. But, if it doesn't get hot enough, it won't release the psychoactive components. Your best bet would be to heat the butter/oil to a low simmer (not a boil) and then add the cannabis. Cook it anywhere from 30 mins to an hour. How much cannabis you use with the oil just depends on how potent you want the butter or oil. If you're using high potency cannabis, you can probably use about 1/4 to 1/2 ounce to 1 - 2 sticks of butter (or 1/2 to 1 cup of oil). The more cannabis you use, the more potent your mixture will be. Hope this helps!

By the way, if you have time for the 24 hour recipe (its well worth it), check out BobBong's post in here on Cannabutter.