@ Rajsekar:

i did not provide any supportive document, i just mentioned that i wanted to visit my family and celebrate tihar at home in nepal which i haven't been able to for past 7 years. According to my attorney, 'visiting family' is sufficient explanation.
since i wanted to visit Nepal mainly to celebrate tihar, i put 11/5/15 as date of intended departure (because tihar started from 11/9 this year) and my advance parole was issued with validity from 11/05/15 - 02/06/16, which is only 3 months. i am also given multiple entry permit for this time period so i am allowed to travel to nepal more than once within this 3 month time period. someone i know also applied for advance parole through tps and his advance parole has validity of 1 year.
it took 1 month for them to issue advance parole for me.
hope this answers all your questions.