The last few weekends I have run some high mileage paths, of 16 and 18 milers. After those, I would go on the MVP for either 45 or 60 minutes.
I have not noticed a difference between 45 or 60 minutes, except that the incidence of approaching numbness in my feet is higher for 60 minutes than for 45 minutes. Otherwise, recovery seems to be about the same for the day after.
For 30 minutes, it seems that there is a difference between that and 45. It would seem that there is a bit more soreness the day after but not sure.
I may try sitting in the MVP for longer and see if there is more effect or not much difference. I may also have to adjust the rest period at the end to help reduce numbing of the feet.