Probably a stupid question... (Timer/setInterval related)

Hello everyone,

I am working on editing this old file from pixelfumes/mudd i believe that has the card flip effect. I basically need the function to occur every 20 seconds (flipping from front to back - back to front). Ive been messing around with different things like setInterval and Timer functions but nothing seems to work. Here is a link to the original files: the effect is perfect for what i need, i just cant get the function right.

Thanks for everyones time and help.