Improve my JavaScript countdown timer

I built a countdown timer in JavaScript that currently works with static logic, but I need it to work dynamically based on different event values I add into a JS object. It will be the same schedule every week, so I just adjust when the events occur each week and it should automatically show the correct content as the time changes. I currently have the listener set up using setInterval but would prefer a more elegant, clean solution that doesn't exhaust the browser as much by running a block of code every 0.5 seconds. I can provide the current code when you message me. This is ALL Vanilla JavaScript— NO jQuery.