I had a lot of asks over the 13th panel and had to bite my tongue for all of yesterday. By now it’s been figured out or decompiled so here’s the explanation anyway along with a bigger still and neat things below.
It plays anytime between 2am - 3am local time. You can change your computer time to speed it up.
The other way is to click the panels on Pinkie’s page to get to the puzzle page. Set the clock to 3, click on the butterfly twice then on the roman numeral 2. Solve the jigsaw upside-down and the 13th panel will play.
The solution above is on the wall.
GIF / WEBM