Drag-and-drop next slide

I built a free form drag and drop with only three items to be matched up to the three choices. For the results, the incorrect default was fine. But, for the correct answer, I wanted to have an explanation as to why each was the correct choice. As such, I built three different layers with triggers showing the correct answer for the corresponding correct drop. The problem is that I can't figure out to to progress to the next slide once the payer gets all three correct. Typically, that would be done with a simple trigger telling the system to jump to the next slide. Not in this case since there is no predicting which of the three items the player will select as their last item. So, I added a 'Drop Correct' state to each of the three options, then built a trigger telling it to jump to the next slide when the state of all the callouts are 'Drop Correct'. That would work just fine except when you come to the last correct option, the system immediately jumps to the next slide without showing the final layer with the correct answer and reasoning why it's the correct answer. It's like I need a way to tell it to wait 20-30 seconds to give the player time to read the reasoning before it progresses to the next slide. Help!