When purchasing online subscriptions, many credit card services will delay payment for processing, and sometimes may also initiate an authorization charge. This is an anti-fraud feature, which validates that the card is real, and is active. The charge, if present, is typically for $1 USD (or equivalent).
Regardless of whether or not the authorization is declined, this amount is reversed immediately. As it's a standard reversal, it could take 3-5 business days for the reversal to be reflected on your statement; however, since it's done within your credit card company's own network, it's typically much sooner. If you don't see this charge returned to your account by the end of the term above, you'd need to speak directly with your card company for further assistance.
Please note that just because the bank approved an authorization charge does not guarantee approval of the purchase. You may need to specifically instruct your bank to allow charges to go through without any delay for these transactions to succeed.