何時可以FILE i485

Hi all,
Here is my GC application information:
I am in EB2
1. PERM Fill date( 3/17/06) Approval Date (4/26/06)
2. I140 File date (6/5/06) LUD (7/29/06) (NEBRASKA SERVICE CENTER)

I would like to know when will I be able to fill the I485, I ask my lawyer, and they told me that I can only file the 485 when the visa bulletin move to the 3/17/2006, which is my priority date, is this true?

Thank you very much for any advise