Should take @ 4 hours.
better start at 6.30am or so.
Its better to wait an hour at airport than to be in panic if some small problem on way
3 hr is an ideal time,start any time between 6:30 and 7:00 and you would reach airport comfortably.
Yes it is only 90 kms and will be easily reached by 3 hours but when people have tight flight schedules we say 3-4 hours because sometimes there will be long unknown jam on the Rohini highway. So precautions are better then cure, I guess.
I have a flight from Bagdogra on 27/03/2016 at 2-15PM.
Please guide when should I start from darjeeling .
Start around 8-9 am and you would reach easily on time.3 hr to reach Bagdogra and check in/baggage drop counter of your flight opens at 12:15.