The problem is when someone enters when it says 60 minutes whether it was longer or shorter for that person tells you nothing about what they're likely to be like later. Generally - the consensus is that actual wait times are a little lower than what is posted (especially as you get very close to closing when you see large drop offs in the number of people entering the lines generally compared to the prior hour). And that is to be expected assuming that Disney builds a little wiggle room into their projected wait time to take into account the many things that could happen to cause the wait to rise a bit. So if the ride continues to operate at full capacity and you didn't see a random huge influx of people at the same time you will have a lower wait. But there are ride breakdowns, and wheelchairs, and large groups, etc. that can throw everything off.
So I'd say having read this board for about 20 years and my own personal experience, I'd say you'll find about a bit more than half will they usually find the wait times a little less than what is posted. I'd say another 30+% of the time they're pretty darn accurate within 10 minutes either way. And then there will be those times that are longer. And often when the wait is longer, you'll find that when you get off the ride it will show a more accurate wait time - but the data just hadn't caught up by the time you entered the line. So you could get on line when it says 20 minutes and 2 minutes after you enter it jumps to 50 as the data makes it way in. Those are the unfortunate situations.
