Black_Star,
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.0/jquery.min.js"></script>
</head>
<body>
<input class="birthDate" type="text" value="22.04.2017">
<input class="birthTimeDate" type="text" value="12:00">
<button class="confirmButton">узнать прошедшее время</button>
<script>
window.onload=function(){
var myDate = $(".birthDate"),
myTime = $(".birthTimeDate"),
fullDate, fullHour, fullTime;
$(".confirmButton").on("click", function(event) {
fullDate = myDate.val().split("."),
fullHour = myTime.val().split(":");
fullTime = (new Date(fullDate[2],--fullDate[1],fullDate[0],fullHour[0],fullHour[1])).getTime();
alert([fullTime, new Date(fullTime)]);
event.preventDefault();
});
}
</script>
</body>
</html>