There are about 20 daily services to Ooty by both Tamilnadu and Karnataka state transport corporations. Both of them operate from the Mysore KSRTC bus stand located in the city center. Out of this about 12 are operated by KSRTC.
The class of services vary. Four of them are Bangalore to Ooty Airavat (AC Volvo bus) services via Mysore. One is in morning (9.30am) , Two are in the noon (12.15 pm and 1.15pm ) and the last Volvo bus to Ooty from Mysore is by 5.30pm.
There are 3 Rajahamsa (non AC with reclining seats ) services from Mysore to Ooty. The first one is at 7am and the rest two are in the midnight (11.30pm & 11.39 pm ).
There are 5 express buses by KSRTC at regular intervals spanning over the day (8.30am, 9am,10am, 12.35pm,1pm).
In short you will find a KSRTC bus to Ooty every hour from 7am to 5pm. And a few more in the midnight. Ticket cost and traveling time varies according to the service. Typically its is between 4½ and 5½ hours. Ticket costs are about Rs85, Rs123 and Rs184 for Express, Rajahamsa and Airavat respectively.
In addition to the bus services, many agencies too operate vans and mini buses between Mysore and Ooty.
Check with the ksrtc website (ksrtc.in) for the schedules and ticket costs. You can even reserve seats online (See KSRTC Booking) through the KSRTC's portal.