When do we think we'll see (if any) returns for this?
There will certainly be a handful. I don't know exactly what their process is for keeping tickets back for sponsors and corporate etc but I think they keep back more than necessary and then re-release what isn't given away.
As for when. You're guess is as good as mine. I doubt we will see anything at all until at least the week before.
The thing is, the demand for the group stages was relatively weak. Salzburg dropped to 1 and I'm almost certain Genk and Napoli didn't even sell out as tickets would be on the site for hours and even days and not seem to get picked up. There really shouldn't be that many people on 3 credits total.