If i had burds on my doorstep then i'd go for more shorter bookings. just to add variety if nowt else
But when its like 45 mins+ travelling each way & other costs i tend to go for 30 mins
The key thing is that you know what works for you
Some of the roma / EE burds who don't speak much english say stuff like 'i want your milk'

I make a point of making sure the burd sees me looking at my watch when getting my clobber off
So when very occasionally they try & rush things along i just look at my watch again & show them. The cool ones usually laugh & have that certain smile. They know that i know the score. And they are then usually much better
Normally 15 min punts are good for me, but she just took the piss telling me to cum after a few strokes but after I spoke to her and she laughed it off it was cool.