Hi Sue! I know what you are referring to but I'm not aware of a schedule that is posted. All my research is indicating "various times throughout the day." However, I'm not sure if I've been just lucky or not but it seems that every time I have been there during my last few visits, the board has been available! You can always ask a cast member of the schedule for that day if you find the board is not displayed when you visit.
In case you didn't know, most of the resorts also have pin boards that they bring out at certain times. Again, I don't believe these times are published but, as an example, my kids and I stopped at the Polynesian around dinner time one evening and it was out and we decided to stop at the Grand Floridian and then the Contemporary and we found a pin board displayed at those resorts as well. Again, probably perfect timing but be sure to ask a cast member working in your resort store if they have a board and if so, the schedule of appearances.
Disney also hosts Trading Nights - you can find a list of current pin trading events
here.
I hope this helps your DD with her pin trading! Diane