Apps are closer to what they expect then what is happening in reality and very dependent on the reporting system that they use and the dependability of those assigned with the task of keying in that information.
I feel the wait times typically reported are hindsight, they tell us what was and not what is. Touring Plans use an algorithm, and use to be pretty spot on. Last year though, both in September and November/December they were off much of the time. I will see how they do this year. WDW reported wait times seem to be off more of the time, even years ago.