You can sign up whenever you want. You will always pay the current month's price at the time of sign-up and your membership will always be active for one full month from the date of purchase. For example, let's say the price for May is $30/week. If you sign-up on the 1st of May, your membership would expire on the 31st of May. If you signed up on the 20th of May, you would pay May's price of $30/week and your membership would expire on the 19th of June. If you then decided to sign-up for another month on the 25th of June, you would then pay June's pricing, with your month expiring on the 24th of July.