Why are they limiting themselves to starting on the top and bottom of the hour only? Not a customer so don't know but is that how they actually schedule?
I find it unlikely that they would wait until that time for a 30 minute appointment, but apparently schedule hour appointments at other intervals, e.g., 10 after, 20 before.
But just assuming, observations that time is not the driver of prices aside, if you assume a 10 minute between session standard for the 6 hours the ad indicates she is having 5 hour sessions (total rev 1400) or 9 half-hour sessions (total rev 2160). Is you view that this "wild discrepancy" is that the hour sessions should be priced at about 430 (based on revenue potential for the 30 minute sessions) or 480, double the shorter session rate? Or that the half-hour priced at 155 (based on revenue potential with the 10 minute breaks) or 140 as half the hour rate?
I think those types of simplistic approaches ignore some important aspect -- relative demand for session lengths, i.e., what volume to expects daily, profit maximizing prices for the longer and shorter session demand, and quantity of work, think overtime compensation perhaps - almost double the work in terms of customers seen. On that last bit, and the comment about pricing not being about time, perhaps they have a target number of customers they are expected to see, for the sake of the argument as max possible for hourly customers, an then get some premium pay if they are making themselves available for those additional 4 potentially available if all are 30 minute sessions.
All a hypothetical story for discussion here but wondering about your thinking on why these rates are so wildly discrepant.