Retrieval Assistant Pricing

Hello everyone,
I’d like to try the new Assistant API for a retrieval purpose, but I have no clear the pricing.
I have only read that it is $0.20 per GB per assistant per day.
I have no clear the “per day” constraint.
For example, if I create an assistant and I store 1 GB on day 1 and two people use it, it’s $0,40 (excluding the classic input/output pricing I suppose).
What if on the second day nobody uses it? Do I have to pay $0.20 again?
Many thanks.