need clarification for 180 days calculation

xstone

Registered Users (C)
Guys.

Assume I filed I-140 and I-485 petition concurrently on July 1, 2003, and my I-140 got approved, for example, on Feb 1, 2004. Then my spouse filed I-485 with follow-to-join on March 1, 2004.
I am wondering when is the earliest date that I can change employer safely using AC21. I understand that date is either I-140 AD or the 180 days after I-485 filing. I should take whichever is late. But I am not sure the 180 day is based on my ND or my spouse ND. Can anyone clarify this? link and reference are very appreciated.

Thanks.
 
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