No-one knows about your graduation date other than you.
But Adobe will send a re-validation email when your current membership approaches its renewal date. Then you can elevate to a standard membership (and pay the increased monthly fee).
http://www.adobe.com/products/creativecloud/faq.html
How do I revalidate my Creative Cloud Student and Teacher Edition membership each year?
Customers who purchased the Student and Teacher Edition of Creative Cloud directly from Adobe will receive an email regarding revalidation 60, 30, and 7 days before their renewal date. The message will direct the customer to a validation page on Adobe.com
If you are no longer eligible for education pricing, you can easily move to the standard membership. The revalidation email that is sent 60, 30, and 7 days before your renewal date will also include the option to elevate your membership. If you choose to do so, you will be directed to the Account page on www.creativecloud.com to sign up for the annual plan at US$49.99/month.
So if your Cloud membership expires, say, 3 months after you graduate then you'll get an extra 3 months at the Student rate until you can no longer validate that you're a current student. Then you upgrade to standard membership.