Applications for the May, August, and December ceremonies normally open in late February, mid-June, and late September respectively. Once confirmed, exact opening and closing dates are noted on the Graduation Ceremony dates and application opening and closing dates page:
It is important to note that there is a limit to the number of people who can graduate in person at any one ceremony and applications may close earlier than the stated date if this limit is reached. There is no limit to the number of people who can graduate in absentia, but your application must be made by the closing date. Late applications, whether in person or in absentia, will not be accepted.