H1-B stamping and extension

[RKON]

Hi,

I have my H1-B visa stamping that is valid until Sept 2020 with employer A. If I change my employer to B and if I travel to India after the transfer is approved, do I have to attend stamping interview again?

I got my stamping in June 2018 and I am planning to travel to India in November 2019.

Apart from this question about the stamping, I am also wondering if how long (months or days) the current H1 should be valid in order for me to file an extension?

[gopalakrishnach]

No need of interview. Just carry old stamped valid visa and new approved H1B.

Normally  6 months before expiry.

[RKON]

Thank you, Appreciate your response.