The newer places will oftain give the girls up to 1/2 the door fee in order to keep tham wortking while things are slow. Once a place gets going usually $10-15 for the first 1/2 hr is plenty, plus $5 for each additional 15min.
Thats why a good desk person will always try to get you to stay as long as possable, while the girls prefer the quick turnover.
In some places the receptionist is paid extra for sessions over 1/2 hr.