H1 transfer right after approval of extension beyond 6 years

[sunnsm]

Is there is a minimum time limit before which an approved extension of H1 beyond the 6 year limit due to an approved i140 can be transferred?

I did get 3 year extension beyond the 6 year limit with an approved I140 recently. I came across a better offer from another employer and was thinking how long should I wait before I approach the new employer to transfer the H1. Is there is any limit?