I would guess and suspect that they do monitor waiting times.

However, this seems to not be that much of a priority. Yes, most of my calls have had me waiting more than 20 minutes, at which point after 30 I hang up.

Speaking of hanging up, when asking for flight status information, on two occasions, they hung up on me. Some of those people in that call centre are quite rude, cold and are a disservice to the SQ Group. However, there are some very friendly people. This does not cancel eachother out though.