May 12th is the campus wide ceremony with the Chancellors lunch right after commencement 11:30-1:00.
The College of ACES ceremony, held on Sunday, May 13, information is here https://graduation.aces.illinois.edu/ceremony. The convocation on May 13th is the ceremony where your name is called, you walk across the stage and receive your diploma while in full graduation regalia. That is the Sunday ceremony at 5:30 pm. You will need to order your cap and gown and make sure you are on the pending degree list. You will receive a reminder from Karen Claus (kclaus@illinois.edu) in the spring, but planning ahead is wise, especially if you are interested in staying overnight in the Urbana area.