Temps play a role, and you are both correct.

When I use a crock pot on low, I leave it overnight, and then PRESS all the butter out of the herb with a potato ricer.
When I use the mason jar method- put the weed in a mason jar with butter and water and immerse up to the shoulders in simmering hot but not boiling water, I give it 30-40 minutes and then squeeze it out.

Check out the 'how I make washed cannabutter' sticky in Edibles for a pic tutorial!