Will suggest,
Day1: Take a KSTDC tour to mysore. 1 day trip, starts early morning, and returns by 11pm. They will cover all the places of interest.
Day 2: Take the 0.5 day or even 1 day KSTDC tour of bangalore.
Details here:
http://www.karnatakaholidays.net/city_holidays.htm
Day 3: Visit commercial st. Have south indian lunch at woodys and if you are a foodie, visit food St in the evening (it opens after 8pm). All local food stuff...but worth the experience.
Regards,
Mohit