Transfer I-140 to new employer

[natr_2002]

Hi,

I'm currently on H1B(expires Oct 2021) with I-140 approved( in 2011) from employer A and i have been offered a new role with employer B and they agreed to do H1B transfer and after an year of employment they would start the GC process so if i'm not mistaken employer B has to file a new Labor along with new I-140 which i can port the priority date to this and my question is if my priority date becomes current before they start the new Labor do i miss the window to apply for I-485 altogether or i can still apply for I-485 once i have the Labor approved.

I have been with employer A for past 13 years with not much growth and my priority date is Jan 2011 and finally i made up my mind to switch to a new employer in hope of good prospects and a better life etc, i'm worried if there was a slight delay in employer B starting my Labor and if i will miss the opportunity to file my I-485 before that.

Can someone please advise.