Ah okay - and the 24 hour minimum rental time doesn't apply to VMs? Im just curious how they are getting around the limits that Mac Stadium and AWS have.

They aren't getting around any limitations. How you decide to bill for meeting the limitations is a business decision, and you can do it via either higher average rates and allow more granular rentals to be financially covered that way or by requiring a 24 hour minimum.

I.e. just because Apple requires you to do things in 24 hour increments does not mean your billing has to expose it in exactly the same way.