To subtract minutes to a JavaScript Date object, use the setMinutes() method. JavaScript date setMinutes() method sets the minutes for a specified date according to local time.
Example
You can try to run the following code to subtract 20 minutes.
<html>
<head>
<title>JavaScript setMinutes Method</title>
</head>
<body>
<script>
var dt = new Date("December 31, 2017 11:30:25");
dt.setMinutes( dt.getMinutes() - 20 );
document.write( dt );
</script>
</body>
</html>