What are the times during which buses operate from Gilimanuk to Denpasar. Are there overnight buses
Both the Java-Bali ferry to Gilimanuk and connecting buses onwards run 24/7. I'm not aware of a fixed schedule but you're unlikely to have to wait more than 30 min.
That said, bus travel at night in Indonesia is best avoided, the roads are not great and neither are the drivers. I would recommend crossing during daylight hours if you can.