Hi Anwesha, October to December is the ideal time to visit Bhutan as the air is clear and fresh with sunny skies. January and February are colder, but from then until April the climate remains dry and pleasant and in late spring the famous rhododendrons bloom spectacularly, flooding the valleys with colour. Heat and humidity increase from May, and from June to September the monsoon rains cover the mountains. If you're interested in seeing the rare black-necked cranes, we recommend visiting the Phobjikha Valley between late October and mid-February. I have also attached an itinerary for Bhutan curated by travelers on Tripoto. Please click on this link- https://www.tripoto.com/trip/a-journey-to-the-land-of-happiness-449297 Hope this helps!