What is the last minimum time for apply for visa extension

Need valuable input on below situation

My visa is getting expired on 1st APR 2017 and my family is in India , so have not started my visa extension yet as have planned them to get here and then start filing otherwise they will be blocked

  1. what is the maximum time should i look for before i start filing my visa ? as need to check for the appointment date

  2. will there be any issue for stamping request for my wife and visa for my newly born son as there are only few months left

Congrats on newborn.

You can safely file the H1 extension as long as you receive its receipt notice before the expiry of your current visa. In other words, safely around 2 weeks before the current visa expiration but the earliest would be the best with in 6 months of the current visa expiration date.