It is correct the journey duration will be 1h35min from Malpensa T1, you will need to follow the sign and the elevator at terminal 1 for trains, or Malpensa Express (Train link for Milan). Once you are at the train stop, here will be two binary, you will be able to understand which one to use by reading the info board (look for s50, not MXP).
The 240min you mentioned is the duration of your ticket. Any Transfrontalieri ticket by TILO is valid for 4 hours.
Be advised that today and tomorrow (7th 8th) in Italy here will be strike on transportation so if you are travelling tomorrow your journey might be delayed.