Grace days of stay after 240 days extension? Is it legal?

My 240 days of visa extension stay will be over now. Can i stay for some grace days while awaiting my H1b visa extension result? Is it legal? will it create any problem next time when i will travel to USA? How many grace days i can stay in USA?

There is no grace period available after 240 days wait. You should have upgraded to PP as your 240 day limit was approaching.

Read this article - http://www.murthy.com/2016/05/23/status-inquiry-on-delayed-i-129s-after-210-days/