you can cover Mysore in 3 days. one day for mysore palace and jagannath palace, next day Srirangapatnam and other local sight seeing and in evening Vrindavan garden and on third day a must watch Mysore Zoo and lake boating near that Zoo, if you have plan to during ganesh festival then go to Mysore palace during evening also as you can get to see full lighting on palace which is lucky to see.only four days in a year.(Ganesh chaturthi is one of them)