A booking's a booking. You're certainly under no obligation to give them some money back, not when you've allocated 1 hour, and probably pushed back the next booking to allow for it. These guys are just trying it on.

I notice that half hour bookings are very common in Ireland, whereas they're not in the UK. I spent most of my punting career in the UK, and most escorts over there don't even do half hour bookings. The brothels do, but indie escorts rarely do.

My advice: just say no.