How much time to give Ortygia really depends on YOUR interests. FWIW, I spent 2.5 very fully busy days in Ortygia, counting my time in Siracusa itself. I did not visit Noto from Ortygia – I spent a night in Noto (not counted in the 2.5 days just mentioned). If you want to visit it from Ortygia, I would think you would need to plan on at least ½ day.

Noto is easily visited by public transportation – bus or train – from Ortygia / Siracusa. Ragusa Ibla and Modica generally require a car or a great deal of time and patience.