I work for compA, who sponsors my GC under EB3 (April 2004). I applied for AOS in July 2007. till with compA. I am on H1B now with CompA.

CompB started my PERM for future employment in EB2, subsequently my PERM was certified in July 2011 and I-140 was approved last week with PD ported to my previously approved I-140 (April 2004).

CompB is insisting me to join at the earliest so that the interfile request is send to USCIS for date porting. My intention is to join company B once my 485 is approved.
Q
Does interfile happen automatically?
What is the better option? Joining compB before my 485 is approved (or) wait until until485 is approved and join company B at later date
Will there be a problem to compB (or) its employees, if I do not join them before my 485 is approved