I did it in one day and it was hot, but i loved it. Best gauge would be Siem Reap, were you happy with one day and a bit, then a morning and an afternoon for both in Jog will be fine. I believe after the first dozen sites I have become very good at these, if the guide goes off on some tangent I bring him back to the point. I love the Indonesian school children at these sites, they want to practice English so they introduce themselves to you and ask questions. After the first half dozen you lose interest though