Learn Hardcore Indonesian: Prosesi wisuda dimulai pukul delapan pagi. - The graduation procession starts at eight in the morning.

pagi: morning (approx 04.00–10.59)
siang: late morning / early afternoon (approx 11.00–14.59)
sore: late afternoon (approx 15.00–17.59)
malam: evening / night (approx 18.00–23.59)

You can sometimes hear just “wisuda” used to mean the whole graduation event, but “prosesi wisuda” sounds a bit more formal and emphasizes the structured, ceremonial part of it (the march-in, speeches, diploma-giving, etc.).

Why is “dimulai” used instead of “mulai” or “memulai”?