If you complete your degree earlier than expected, the Student Visa Compliance Team will inform UKVI of this and withdraw your Student visa sponsorship. UKVI will then write to you with a new visa end date. Please note that we cannot tell you specifically when UKVI will shorten your visa as this is a UKVI process in which we have no involvement.
If you are eligible for the Graduate Route visa, the Visa Compliance Team will also inform UKVI of your successful completion of study. You'll receive an email from the team to confirm once UKVI has been notified.