Kharghar is located on the outskirts of Mumbai. It lies in what is commonly regarded as the Konkan part of Maharashtra and fall in Raigad District. It lies on the Harbour Railway, a part of Mumbai suburban railway system. Local trains of the Harbour Line in the Central Railway ply between Kharghar and Chatrapati Shivaji Terminus stations and the Western line is connected through the Wadala station. It takes about 65 minutes to reach Kharghar by suburban train from Chatrapati Shivaji Terminus. For Bandra[W] you need to change at Wadala Rd. to head to Bandra direct. The time taken from Kharghar to Wadala to Bandra would be about 55m journey time alone. You have NMMT buses plying to Kharghar railway station and also local autos. Check if you get share autos. I presume you do.
A drive by road Bandra[W] would be 38km and could take not less than 1.5hrs. Although you drive through some arterial roads, the traffic isnt mild. Hence, nothing less than 1.5hrs.
Depending on the BEST/NMMT buses alone would mean you have a lot of time on your hand. :) Jus kiddin.... It would take a long time and also the buses are limited. You can take the NMMT bus to Belapur CBD and then take bus to Bandra [W]. Route no. 505 takes you direct to Bandra [W] from Belapur CBD.
Best way....
1. Bus/auto to Kharghar Rly. Stn.
2. Kharghar to Wadala Rd on Harbour Line by Panvel-CST Locals
3. Wadala Rd. to Bandra on Harbour Line by CST-Andheri
For more:
http://en.wikipedia.org/wiki/Kharghar#BEST_Services
http://en.wikipedia.org/wiki/File:Mumbai_suburban_rail_map.svg
http://www.mumbai77.com/City_Info_Guide/Harbour_TimeTable.html