it doesn't matter when you start using it, but you'll be charged $ as soon as your subscription begins (whether you use it, or not), and your subscription will end (or renew) on the subscription expiration date.
ie, don't start your subscription until you're, at least, ready to start learning how to use the programs for which you're paying.
So you mean I can start using CC even after 6 months I will buy it? I find discount seles on Amazon, But I want to start using CC after 6 months from now.
beware of scams when purchasing anywhere other than adobe.com
that said, if you buy a one year subscription today it will expire in one year whether you've been using it for one week (a trial), or you start using it 360 days from today and only use it for a few days.