To make it more complete and better aligned with the booking time, you should include 30, 45, 60 and 60+ mins options as well.
Also for clarity, how long do you last on average, should say for straight/continuous banging.
Paying for MSOG should be a factor too.
The excitement of visiting a provider tends to have someone shoot too early.
I usually pay for the hour, and ask for MSOG extra if it's not a part of the main rate. I mean, sure you can whack off before seeing a provider, but seems kind of redundant, right?
Spend the first minutes having her work out that first shot, get the nerves out of the way, follow it up with a few minutes of pillow-talk, then go for the main event until the clock runs out. So 5-10 minutes on the first shot, then 30-50 minutes shooting out the second.
That said, even 15-30 minutes sessions, serve their purpose for one-pump chumps too...