At the time of purchase. When purchasing a subscription, you will be charged upfront.
All subscriptions are billed upfront and on either the one-month, three-month, or one-year anniversary of your initial payment. We do not offer single-term subscriptions. In addition, refunds will not be provided for any subscription purchases, including unused time.
Once you have purchased a subscription, details, such as your renewal date, can be viewed through your settings. See Where do I find my current subscription details?