According to the documentation there are two plans:
Default plan clients:
There are 2,500 free requests per day, a combination of client-side and server-side requests; A fee of $ 0.50 is charged per 1000 additional requisitions. It has a limit of 100,000 requests per day.
Maps API Premium Plan Customers:
Shared free daily quota of 100,000 requests per 24 hours; Additional requests applied against the annual purchase of Google Maps API Credits.
Google provides a virtual calculator for credit simulation: Link to Calculator .
Google provides a monitor to monitor the use of the APIs
Regarding time zone: There is no specific time zone for use and renewal is always done at midnight Pacific Time (PST). "I think it's 5 hours less than Brasília"