Please help: should I apply I-131 for my parents?

If my parents came to USA 2 months ago, I am submitting the applications for their green cards.
can I apply 1-131 for them as well and put "08/20/2014" for Date of intended depature" for 3 to 4 months ?

Will USCIS officer consider them staying USA for just 3 to 4 months if I put above date?

How to fill out the Date of intended depature?

Thanks.