Agree, I have rarely seen show times change.
Unless it is a much busier day than expected and they may add showtimes due to the crowd.
Adding shows, "day-of" is really a separate issue than the one asked by the OP.
(That of show-times changing from those posted a couple of weeks away.)
It is rare that any additional shows will be added day-of for anything except Fantasmic! or Rivers of Light.
Otherwise, I have to say that while I do LOOK at the show-times a few weeks in advance of any trip, I do not TRUST those show-times to
be the same during my actual trip.
Some certainly WILL be the same, but I find that they can and do change performances and times, especially if your trip
comes at the beginning of a "new season" at WDW.
There's a good reason why Disney prints and distributes new "Times Guides" every week (or every two to three weeks) that
offer the most current times of shows, etc.
They can be changeable enough that there are websites that update and repost the new show-times every week on-line.
So, use what's posted a couple of weeks out for planning, but, for sure, look at the CURRRENT times
that are posted/distributed DURING your trip.
