I agree that discounts for times beyond 60 minutes would seem to benefit both providers and hobbyists. I see some rates that are the same per hour for at least the first few hours, some with discounts, and some with disincentives.
A common example is 60 minutes for $300, 90 minutes for $450, and 120 minutes for $600. I prefer 90 minute sessions and might choose either 60 or 90 at those rates. Basically each half hour costs the same, $150.
If the rates are $300, $400, and $500, I'd almost certainly choose at least 90 minutes. I've seen some that are $300, $500, and $600. The first additional half hour costs $200, which is an hourly rate of $400. I would not go for 90 minutes with that pricing. Maybe there is a preference for rates in hundreds, but charging more per hour for additional time will not make for longer sessions.
A provider in another city just raised her rates by $100, but with $400, $500, and $600 for the 3 durations noted above, I have not lost interest because the extra 30-60 minutes are a bargain.