Like I mentioned, we had the IQ done two years before the skip came along so they were two different processes. For IQ, I think that it took a few weeks before we got results. For the IAS/skip process, the whole process played out over a month or two. It has been a while (dd14 is a 10th grader now and was in 4th grade when the school was evaluating her for a skip), so I can't recall for sure. However, I believe that I wasn't too concerned that they were going to say "no" since they were the ones who initiated it. We were more the ones who needed convincing and we left the meeting at which they approved the skip not having made a decision and telling them that we'd discuss and get back to them.
I can see as how this whole process may be a lot more stressful in your situation since you are waiting on test scores and the school may not be as gung-ho behind it. In regard to whether IQ supports achievement, though, I can say that I've seen it both ways but it is a lot more likely that you are going to see achievement higher than IQ when you are dealing with achievement that isn't as high as your ds'.
For instance, I've seen high achieving, but not gifted, kids who are pretty consistently A students in grade and who get grade level achievement scores that generally run around the 90th-95th percentile and which even sometimes pop up to the 98th or 99th percentile. I think that above level tests can help tease out the high achievers like that from gifted kids to some extent as they really become more of aptitude tests than achievement tests when they are taken a few grades above level like your ds did.
I'd bet that, with as highly as he scored on the Explore, there is a very good possibility that the IQ scores will come in where you need them. Not hitting the IQ bar on the IAS also doesn't rule out subject acceleration, but I'd expect that his chances are good on IQ none the less.
