Every parlour salesman wants you to be able to milk in 90 mins. I guess they have no vested interest in selling big parlours.4 hours on your own including getting cows in and washing down maybe. With 2 people absolutely not. That's 16 hours of milking a day. Plus in a parlour of that length you will spend more time walking up and down than milking. Every parlour salesmen I've spoken to aims to design a new parlour to have it done in 1.5 hours tops plus wash down.
12 sides here. 1st 10 sides are a breeze last 2 sides your ready to finish.
Stick 2 in the pit and 16/18 sides wouldnt be a problem but there would be a lot of waiting around.