Show Layer when buttons visited AND timeline ends

I have a slide that I don't want the learner to be able advance to the next slide until they select ALL of the 5 buttons on the slide AND the base layer timeline ends. I have created a special Next button that allows them to advance to the next slide in a separate layer. I tried creating a trigger that the Next layer shows when the timeline ends and a trigger to show the Next layer when all five buttons are in a visited state, but that didn't work. I tried creating a variable counter that adds 1 when the learner clicks on a button then added a trigger to show the Next layer when the timeline ends with the condition that the counter = 5, but that didn't work either. I'm stumped. Any suggestions?