Per hour billing of Microsoft hosted azure agents?

Hello!

I am a bit confused about where to best post this, if this is the wrong forum I apologize and ask that you redirect me.

We recently felt the need to scale up the number of Microsoft hosted build agent in azure devops. As a way of limiting cost, we wonder if we can enable/disable agents during the night?

Ergo, run 12 agents during 8:00 -> 16:00 and then run 3 agents 16:00 -> 8:00.
Would this setup lower our bill, or is the agents billed per day?

Any insight is appreciated!