Cut like that with a large, sharp saw could be done in 5 mins. If the bar was long enough to cut from one side, it’s 3 cuts only. If there was no notch/scarf, one backcut and could be done quicker than 5.

Source: Arborist. Our 30 year old trees are that diameter so we get a lot of practice.

Your questions still stand but it could be fast if it wanted to be.