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>
$(function(){
$(".confirmButton").on("click",function(event){
event.preventDefault();
var date=$.trim($(".birthDate").val()).split('.'),
time=$.trim($(".birthTimeDate").val()).split(':'),
fullTime=(new Date(date[2],--date[1],date[0],time[1],time[0])).getTime();
alert(fullTime);
});
});
</script>
</body>
</html>