It is the number of days before the end of the billing cycle on which Sprwt starts trying to charge the renewal. Example: a 1-week plan renewing on Sunday with a buffer of 3 days will be charged from Thursday onwards, so the kitchen knows the order is paid before planning the next week.

The automatic renewal job picks up a subscription as soon as today falls inside the window that starts buffer days before the renewal date and ends on the renewal date itself; if the renewal date has passed and the last attempt did not fail, it keeps trying. In the plan's Current Subscriptions table a renewal date highlighted in yellow means the subscription is inside this buffer window; red means the date has already passed.