Is there any timeline in which visa must be transferred to current employer?

I got H1B visa filed by my previous employer (while I was in US) which is valid till Dec 2017. I have joined a new company within India now but they are not much interested in visa transfer. As my visa (filed from my previous employer) is valid till Dec 2017, does it mean my new employer can file for transfer anytime before my visa expiration date and it will be valid till then or else there is a timeline in which a visa must be transferred to my current employer?

Another employer can file a cap-exempt petition for you within 6 years of last date you were on H-1 status, or 6 years from effective date if you have never been to US.