Intended date of travel

Hi my wife will be applying for a spouse settlement visa soon,

My question is on the .gov.uk website i read somewhere that you can apply 3 months in advance of your intended travel date.

on the visa4uk website it gives you the option of choosing a date 6 months from the online application date.

i want to apply for visa in end of november 2016 for my intended date of travel in mid march 2017.

i am applying well in advance as my wife will need her passport on 07 march as we are going on honeymoon from india and back on 17th march.

my wifes intended date of travel to the uk is 21 march 2017.

does the 30 day visa start from the intended date of travel or from when the visa application is granted

It should start on the intended date of travel but many applicants have not been fortunate to have this done and UKVI have issued from date of decision which then involves trying to get it corrected, which also takes more time.