Bus services are available all through out Goa between 7am to 7pm. Main bus stations of Goa are Panjim, Maregao and Vasco da gama. Very frequent buses are seen at Palolem beach, Baga, Anjuna, old Goa and near railway stations. You could enquire at the hotel you stay in Goa, or at main bus stations who might provide you better info.
Local bus stations are available as per time basis in Goa also as per availability at early morning.
The concerned travel desk / hotel person at particular hotel will assist on same as they've connection with the local bus transportation services over there.