The post count is reset after every 30 days from the day you subscribed.
E.g. If you subscribed on 5th April, your post count will be reset on 5th May.
Note: If you subscribe during the 7-day free trial, you'll be billed after the free trial ends. However, your post count will be reset based on your subscription date.
For instance - Your free trial is from 1-7 April and you subscribe on 5th April. You'll be billed on 8th April, but your post count will be reset on 5th May.