There's nothing to feel guilty about.
Just book the time you need.
Generally the rule for me is:
If I'm just going for one pop, with a girl I'm unsure about, book 30 minutes.
If I'm going for two or more pops, with a well reviewed girl, or one I've seen before and enjoyed, book an hour.
A lot of WGs also have a hidden 45 minute rate, that you could ask about.
But definitely don't feel guilty about only paying them £60. Firstly, that's £2 a minute you're paying them. What other job does somebody earn £2 a minute in? Secondly, those £60/70/80 can add up to a lot of money over time.
Also, if a working girl rushes you out the door after 40 minutes, when you've booked an hour, that's not good.
Write a review for them and say that they did that.