JSFiddle - React, Tailwind, and code Playground
JavaScript
var oldDate = '2021-03-10';
var convertDate = new Date(oldDate);
var newDate = (convertDate.getMonth()+1) + '-' + convertDate.getDate() + '-' + convertDate.getFullYear();
var b = '7:45 AM';
var newB = newDate + " " + b;
var bDate = new Date(newB).getTime();
console.log(bDate);