H1B Extension Stamping Before Expiry

[pizfor21]

Hi Guru's, 

My current H1B visa is expiring in March 24, 2016. However I am planning to apply for renewal petition and might have approved one in 3 weeks from now for next three years until 2019. If I am not wrong, the new petition validity starts from March 24, 2016 that is after the expiry of the current petition on March 24, 2016. In the mean time I am visiting India in December 2015 and planning to schedule an interview for the new visa stamping in first week of December 2015. 

1) Can you guys please let me know if I can go for extension visa stamping before the expiry of the current visa. 


2) If 1 is true, How soon Can I apply for the new visa based on my approved H1b extension ? Is there any rule like 90 days before only(for fresh H1b's I see it is 90 day) as I am already working in US and have valid visa ? I am eligible for drop-box so want to drop all docs in December 1st week somewhere 110 days ahead of new approved I-797 start date. Is it Okay ??

 

I am more concerned of 2 here. 
 

I very much appreciate your help on this. Please reply ASAP. 

Thanks in advance,