How to make jquery count down timer function manually editable

I have a wordpress theme and I would like to display a certain promo start time in front page. It uses jquery.countdown.min.js and has following default timer settings

It displays that promo will start in four months later after now. But I would like to set timer manually via wordpress admin dashboard. Is it possible to insert some php codes in .countdown(‘2020/10/10’ something like

so that I can edit promo start time manually

My options are: