How to make universal countdown js php?

Question

PHP

Good afternoon! I really need help, because I have no ideas for implementing this (((
There is an api from which I get a json file. It consists of the name of the store and the end date of the sale. Each store has a different date.
It is necessary that a countdown timer pop up when choosing a store How to make the timer not individually registered for each date, but he himself counted by arrays (after choosing a store), which date he needs to set and count?Thanks in advance for your answer!