Declare Sub Sleep Lib "kernel32" (ByVal lSleepTime As Long)
Sub OnSlideShowPageChange(ByVal oWindow As SlideShowWindow)
' This will fire with every slide change
With oWindow.View.Slide
' Obviously, this isn't what you want to do, but the two values
' will give you the info you need to calculate your 25/50/75% points
' and do whatever you need at that point
MsgBox "This is slide: " & .SlideIndex & " of " & .Parent.Slides.Count
' You could instead display a user form that gives the message you want
' and include a call to the Sleep API above to have it wait X seconds
' then Hide/unload itself
End With
End Sub