I'm sorry, maybe I don't explain myseft correctly. I don't want a premium membership on a daily basis. I want to pay it quarterly. They say the following:
Note: When you cancel your account, it remains active until the end of your payment period. You may still log in and use Second Life during this time. For instance, if you buy a yearly Second Life membership and cancel it the next day, you are still be treated as a premium member for the next year!
http://community.secondlife.com/t5/English-Knowledge-Base/Premium-membership/ta-p/1054477
So, this way, I can control my billing cycle without thinking in an auto renew, meaning I won't be involved in billing issues to the end of the cycle because they will downgrade me to basic the last day of my cycle and I can renew at my own desire.