H1 visa - question on extension filing and travel/stamping

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Hello,

I converted from L1 to H1 visa in 2012 Oct in COS, and since then have not visited India.
I work in EVC model and plan to travel India in June this year for three weeks, and have to do stamping there.
I received my I-140 approval recently.
My current petition expires in Sep/30 this year.

I have following questions please:
1- If I apply for H1 extension and get three yrs extension before traveling to India, can I get that additional three years in my stamping, or I will only get stamping till Sep this year only ?
2- Is there any problem if I file for extension before my travel, or I should do it after I return back ?

Thank you in advance for your time !

Regards,
Himansu