Layoff한 이후에 일자리를 어느정도 기간내에 빨리 잡아야 한다는 어떠한 룰/규칙이 있나요?

저는 I-140가 승인된 이후에 layoff가 되었고 I-485는 pending되고 있는 상황인데 (same job title)일은 잡히지 않고 답답할 따름입니다.

1-140 : Passed
I-485 : Pending

When you get a RFE requesting your status of employment in the same industry, you should be able to provide the evidence that you are employed at that moment in time. In other words, as long as you can respond to the RFE, it should be okay.
This is just an opinion from my experience, use it at your discretion.