Hi, Though 3 days are enough but I would suggest you to give atleast 4 days, because you will be travelling from Dharamsala to Dalhousie also. Give 2 complete days to each destination.
Hey Shree Yes, u can easily visit all the three places in 3 days... Start from Dharamshala and then to Mcleodganj which is hardly 20 odd Kms from Dharamshala and then go to Dalhousie ... Check this blog from Karishma who has done the same trip as you are planning to:- https://www.google.com/amp/s/www.tripoto.com/trip/dharamsala-mcleodganj-dalhousie-2017-58db715f01d82.amp Hope this helps you.... Happy Travelling!!!
Absolutely 3 days are sufficient for covering these 3 areas.
U have to take night journey to reach other place and whole day u can explore the places....