As a nail tech, doing my own...
It always takes me 4 hours to do what I could do on a client in 2!! I didn't even do my right hand, it just has the purple base with cateye cuz I'm not doing intricate layered fine art/filligree with my non dominant hand haha. So let's say 5 if I did full design on both hands.
I've been debating trading or having someone else do them but they're too good and I hand out a card to every single checkout worker wherever I go. So I will spend my entire productive time every other Sunday hunched over my desk like a goblin.