One of the reasons that estimated the single rider line is so difficult, and thus, inaccurate is because of it's very purpose. If the standby line is full of even number groups, your wait will be longer, because you are literally having to wait until an odd numbered group comes along and "needs" you to even out their group. I love how disnut8 above speaks of silently cussing out the even number groups and cheering for the odd number!
CMs aren't going to give you an estimate because of that very problem.....and if they tell you "oh it shouldn't be too long" or give you a time....and then it IS an hour long wait or goes past the stated time, many guests will complain that they were given inaccurate information. The posted times for standby have become less and less accurate, probably for the exact same reason. A guest will feel GOOD if you post the wait time is 45 minutes but they only end up waiting 30 minutes......but they will potentially become ANGRY if the posted is 40 and they wait 45.
I've noticed this phenom a lot in the "real world" too.....especially with Southwest airlines which my husband flies weekly.....they almost always arrive at least 10 minutes before the posted time. Wow, they must have the best "on time" record in the world as they are always arriving EARLY.....ummm, no, they just give themselves some padding every flight.