Test for end time

HTML

<input type="text" class="startTime">
<input type="text" class="endTime">
<button type="button" id="timeAddButton">Submit</button>

JavaScript

var startTime = $(".startTime").val();
var endTime = $(".endTime").val();

st = minFromMidnight(startTime);
et = minFromMidnight(endTime);
if(st>et){
    alert("End time must be greater than start time");
}

function minFromMidnight(tm){
 var ampm= tm.substr(-2)
 var clk = tm.substr(0, 5);
 var m  = parseInt(clk.match(/\d+$/)[0], 10);
 var h  = parseInt(clk.match(/^\d+/)[0], 10);
 h += (ampm.match(/pm/i))? 12: 0;
 return h*60+m;
}

$("#timeAddButton").click(function () 
{
    if(st>et){
        alert("End time must be greater than start time");
    }
});