Help with creating a creating a chrome extension that displays the total youtube playlist time

Hi im fairly new to programming and idk if this is the place to ask

I have created a chrome extension that displays the total time of the playlist on the page. However, my extension only works if i refresh the page. currently, I use a setTimeout function to wait for the page to load before calculating the total time(yes i know its bad) and displaying it on the page. I tried using a mutation observer but i cant get it to work. Does anyone have any suggestions or alternatives i could use?