Its all dependant upon when extras are offered.
If you only have less than 10 minutes of a 60 minute session, what value are you really getting ?
If she offers half way thru, maybe.
But always remember that once you knock her back, you have a 90% chance of having time cut short and shit service.
Best is always say, tell me the price for next time and I can bring the extra cash.
Its an incentive for them to finish properly and maybe something thrown in to entice.
You also find out how many pineapples and have time to consider their off and whether worthwhile returning.