Yes, the date of the graduation ceremony is not relevant for the Graduate visa. The important date is the date that your successful course completion is confirmed on your student record, which will be shortly after the exam board ratifies your award.
Following this, you should receive an email from the Visa and Immigration team confirming that your successful course completion has been reported to the Home Office.
If you do not receive that email from the Visa and Immigration team within 1 month of receiving confirmation of your award (or if you have less than 1 month remaining on your current visa), you should contact us and you should not apply for the Graduate visa until you have received advice from the Visa and Immigration team (immigration-support@nottingham.ac.uk).