The official rule is that if the wait time is 10 minutes or less, the guest will be sent directly to the appropriate queue, which is most likely not the stand by queue, as there may be reasons that the standby queue doesn't work for the individual, regardless of the length of wait. This is what is written on the Disney site that is SueMN has previously linked to.
It has been reported on here that some CMs are allowing people straight in when the line is a 15 minute wait or so, not seeing the point of making someone wait 5 minutes. But that is up to the CM.
My experience is in DL, not WDW, but I have been told to use the stand-by queue for a 10 minute wait, and when I told the CM that it was not safe for me (and explained why, which meant explaining my medical needs all over again at the attraction despite having a
DAS in hand), I was told that I would have to go get a time for "NOW" to be allowed to use the FP queue (which was also a hill, but one without people, so I would do the wheeling all at once, then wait at the top).
This seems to be a point of confusion on both coasts, and seems to vary depending on the CM working the attraction. Even Guest Relations did not seem to understand that it would be a problem for some people to wait in the stand-by queue even 10 minutes - that is may be the physical queue that is the problem and not the wait time. It does not matter to me whether the queue for that attraction is 5 or 55 minutes - I cannot physically do it.
I think this is a learning point, as so much of the focus has been "wait time." Sometimes there seems to be a CMs understanding that "waiting place" may be just as big or an even bigger issue. This is something that, on both coasts, polite but detailed feedback to Guest Relations (make sure they are actually going to submit a report on it, that it is feedback for all future visits and not a complaint that a re-admit pass will fix) will help.
The person I spoke with at Guest Relations had never considered why waiting for the Aladdin show would be a problem. It has 4 fixed show times a day, and therefore no "wait time" to write on a DAS. And when I asked "what do I do for the show" - no one had an answer. I did insist that she make sure her supervisor send it up the chain, so that an answer can be decided for the future, not just for me but for others who want to see the Aladdin show with a DAS who cannot use the regular queue.
Basically, Disney cannot fix it until they know of an issue. In this case, they need to have an answer they can give to Attractions CMs when a guest arrives with a 10 minute wait time and cannot use the stand-by queue.
Since this is a major issue, apparently on both coasts (with GS telling people one thing, and Attractions doing another), I very much hope they have an answer quickly - both for the guests and the CMs' sakes!