The prices look suspiciously cheap for an agency: 1hr: £110; 90m: £170; each additional hr +£100. O/N's £750 That said: they're outcall only by the look of it - so no burdensome accommodation overheads.
If its anything like a normal agency set up, then the agency take will range from c.30% (if it's basically 1 pimp) to more like 40-60% if there are staff with proper support infrastructure.
So, whilst an overnight would see the girl doing nominally good business (clearing £525 at best; more likely c. £375 for 8 hrs), for hourly bookings she's maybe clearing as little as £60.
Something has to give: her availability; reliability, preparation, performance, sobriety sanity or longevity; your satisfaction or the owners earning power. I'd be surprised if it was the latter. So I guess it'll be any combinatiom of the former.