The first payment will be billed immediately. Starting August 21st, your plan will automatically renew on the anniversary date (instead of on the 1st of the month) following the last delivery of your current plan (do not worry, you can cancel the upcoming renewal at any time). So for example, if you subscribed on September 2nd, and you have a monthly subscription, you will be billed on October 2nd, November 2nd, and so on. If you sign up on the last day of the month, your renewal date will be on the last day of the month. You can check your renewal date from your account dashboard.
*Please note, starting August 2017, we're changing our cut-off date from the 20th/21st to the last day of the month midnight PT.