No lawyer even claims that. Please point to a lawyer arguing that it establishes precedence.
Sure.
http://www.usvisahelp.com/art_intent.html
The Law Offices of James D.Eiss
The concept of “intent” is borrowed from Seihoon v. Levy and applied to many other immigration contexts in which the alien is required to have a certain intent.
Even though "precedence" has not been explicitly stated, it is pretty evident. Also, i recommend following it more as a
Rule of Thumb
Based on the above, The Rule of Thumb should be that It is ok to quit the sponsoring employer 90 days after GC approval. However individual circumstances will vary, and one should always consult a lawyer before taking a decision.
Unless you can point to solid evidence for your claim, your conclusion is not valid. Or in other words, you can't conclude anything if the premise is invalid
We dont have "solid evidence" for any anything, including any "rule of thumb". The closest we have is the verdict in Seihoon v/s Levy and the Courts interpretation of "rapid course of events" after getting GC. So as such any premise is invalid, whether 90 days or 180 days. However if we DO need to formulate a Rule of Thumb, 90 days would be a good one considering Seihoon v/s Levy.
Ofcourse one can quit after 6 months, 1 year , 2 years or even 5 years , with progressively lesser chance of any issue, but what we are considering here is the "minimum" safe period of time , considering similar cases prosecuted by USCIS with respect to "intent" and previous rulings given by the Honorable Courts with respect to "good faith intent" in ANY context.
I do however accept the fact that there could be a case in Court tomorrow and the Court could rule that the employee should stay with the sponsoring employer for 2 years atleast to prove "intent". However I see no reason for the Courts to "revise" the time period from 90 days to 180 days or more for immigrants in particular while keeping it as 90 days for non-immigrants to prove "intent" (Will immigrants have "lesser" intent than non-immigrants?!!! ). So the previous 30-60-90 day rule could still be considered for immigrants, accepting the fact that the one cannot predict in advance what the Court will say in a "future case" - 90 days, 180 days, 360 days, 2 years? So, it is imperative to consult a lawyer before taking any decision.