As others have said, overnights can often be not be great VFM. I have done a few in my distant past but always found the WG's want to sleep most of the time after 1/2am, whilst I was in the shag zone all night after a suitable recovery time had set in. I know WG's are not robots, but if you proceed with an overnight be sure said WG is ready to stay up and party all night. If not you are effectively renting pussy by the hour to snooze on your time. If she wants to sleep for several hours it should be reflected in the rate.
Overnights are not for me anymore, I consider them in the same zone as paying for dinner date time. Both are a waste of good punting funds.