Stuck with having a vba only apply to a specific slide

Sorry a complete noob to vba but I'm using a vba to create a countdown timer, here it is:

Please Login or Register  to view this content.

Moderator's note: Please take the time to review our rules. There aren't many, and they are all important. Rule #2 requires code tags. I have added them for you this time because you are a new member. --6StringJazzer

Question:

This creates a countdown timer in the shape named "square" on slide 21 (in bold for ease). The problem is sometimes I change the order of the slides so have to respecify the slide each time, is there a way to have this run without needing to specify the slide? I've tried googling this and apparently the trick is to remove the 21 but this doesn't seem to work. Anyone know how to do this? Thanks in advance.

Take a look here

https://www.youtube.com/watch?v=u2wDxkDmqbU

https://pptvba.com/powerpoint-insert...-vba-tutorial/