The best time to visit Jim Corbett begins from November which goes up to June, but it depends on what you’re looking for from this trip is it great weather, beautiful jungle landscapes, and other animals or too keen to see the tigers? After July the monsoon season starts because of which many a time the forest zones are closed owning to the heavy rainfall received in the forest areas and you may not get a chance to see any tigers but you might probably get some sight of elephants and deers.
For the former, you can visit anytime up till March. After that, the temperature gets high and the animals come out of the forest's denser regions towards the waterholes. This is the perfect time to spot the tiger. You'll be having much higher chances in the summer months.
Wish you a great trip!