What is the processing time required for approved an amendment on already approved EB3 I-140 because of SII?

Will it be placed on the same queue of I-140 application whose approval time involves for years?

You can opt for premium processing which can adjudicate your application in 15 working days.

If not opt for premium processing service, how long it normally takes to get an approval?

Will it be placed on the same queue with initial application for I-140?

Depends on the service center, you need to check current processing times.

Yes.