When does class start tomorrow? vs What time does class start tomorrow?
Bilakah kelas bermula besok?

Pukul berapakah kelas bermula besok? - do we add Pada in front of pukul?

Question

When does class start tomorrow? vs What time does class start tomorrow?
Bilakah kelas bermula besok?

Pukul berapakah kelas bermula besok? - do we add Pada in front of pukul?

Answer

Yes, the second sentence is the correct!

anything that have numbers, like times or currency, you must use berapa.

Answer

When does class start tomorrow? 
-> Bilakah kelas akan bermula esok?

What time does class start tomorrow?
-> Pada pukul berapa kelas akan bermula esok?