JSFiddle - React, Tailwind, and code Playground

JavaScript

var end = '04:30 pm',
    begin = '02:30 pm';

function humanReadableToMinutes(time)
{
    var parts = time.split(/ |:/);
    
    return (parts[2] == 'pm' * 12 * 60) + parseInt(parts[0], 10) * 60 + parseInt(parts[1], 10);
}

console.log(humanReadableToMinutes(end) - humanReadableToMinutes(begin));