This tip is for travelling(in bus) between SHM-SDAH-SHM:
From Sealdah Bus Stand(the one near Big Baazar and opposite NRS Medical College and at the foot of the flyover), there are two buses which take you near Shalimar. They are:
1. Rajarhat-Nabanna(Private Bus): This is a blue colored private bus and can be found more frequently than the next bus I am about to mention. This bus takes the route via Rabindra Sadan and then the second bridge and terminates at Nabanna. However, the disadvantage is that Nabanna is a bit far...
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from SHM and so you have to either take a battery operated e-rickshaw or a normal cycle rickshaw which can be a pain if you have a huge amount of luggage. So I suggest to keep this option at last. The fare is Rs 10 for one person(might have increased).
2. Sealdah-B.Garden: This is a small white colored bus which is your best bet for reaching SHM. Be careful however as this bus is not as frequent and so, you might have to wait. Board this bus and get down at a stoppage known as Shalimar 3 no gate(you can see the tracks leading to SHM from this stoppage) and then follow the tracks for a walk of about 5 mins and you will reach the station. The fare is around Rs 12-15(can't remember accurately) for one person.

EDIT: The estimated travelling time for each of these buses depends on the traffic present on the road. If you are travelling during office hours then I would suggest you keep some time at hand as travelling may take well between an hour and a half to 2 hours due to traffic. In other non-office hours, travel time will be much shorter and depending and you can reach SHM in about an hour.