Thats a tough one my friend. It could take you anywhere from an hour to maybe three. Much depends on traffic and jams. So plan in a manner that you have sufficient buffer in hand. Usually Ola/ Uber apps could give you indications on travel time. You could also look up Google to tell you how long it is taking from Howrah to Dum Dum on your travel day around 10am. That might help you guesstimate.. Best of luck.
Evening Aarti at Daksha Mahadev Temple. Everyone knows of the evening aarti ritual at Har Ki Pauri but not everyone is familiar with the same (or better) aarti experience that you can get at this temple. ...
Bharat Mata Mandir. ...
Kankhal. ...
Lassi at Prakash Lok.
Minimum of 5-7 days if you want to explore all the islands and the offbeat places. Cost would be around 30k to 80k depending on your accomodation, transport and restaurant choices.