Official critique uses a credit system.

The moment you subscribe to a membership level in the Patreon page you will get charged for the respective amount. At the same time you will get the respective amount of credits for that membership level added in drawabox.com website. Credits expire after 2 months (I think) if not used.

You can check how much credits each lesson takes by going to that lesson, clicking on "Submit homework for review" and then clikcing the "Submit for Official Critique" button. That will show a new panel which shows your current number of credits and the amount of credits the official critique for the lesson costs.

Your progress thru the lessons is tracked thru your drawabox.com account and is independent of the Patreon membership. So you can subscribe to Patreon membership, immediately submit your homework for official critique and then cancel Patreon membership (note that by then you already have been charged for the month, and already got the credits in drawabox.com).