My experience has been that sometimes the charge doesn't even hit the card at all if you do the 24 hour cancellation quickly enough, but the rest of the time, it usually posts within a day or two.

I've probably had a few cases over the years where it takes a few days, but probably nothing longer than a week. I'd give it a full week - and if you still don't see anything at that point, I'd definitely give DL a call and have them look into it. It also might be worth calling your bank before you do that just to make sure they don't see anything on their end, since I'd imagine one of DL's first questions will be if you contacted your bank.