where is interview waiver decided, what does processing time really mean

[cclr 6]

We filed for AOS in Dec for my husband. He received AOS and EAD fairly quickly. The website does not update our case, it is stuck on "Jan 27 we received undeliverable mail..." . We have called USCIS and they have the correct mailing address, and the last update we have was that our file was sent to the local office(St. Paul MN) on March 27. We have heard nothing since. When I look at processing times for field offices St Paul is processing Oct 12 cases. I have 2 questions, first since it has been sent to St. Paul does that mean that we will have an interview? Second, assuming we will have an interview and they do cases in order should we expect to receive a letter in about 2 months with an interview date, or would we get a letter sooner with an interview date in approximately 2 months? We have decided on a school for him and want to start him in the fall but from what the school has told us, he will not qualify for financial aid unless he has a green card. I am trying to figure out if fall semester is a possibility or not. Thanks for your help