Adding minutes to datetime in momentjs

moment().format("LTS") returns a string value in hh:mm:ss AM/PM format. When you create a moment object using a string that is not in standard format, you should pass the input format as second parameter to moment constructor.

For eg: Jan 1, 2017 in string 01012017 is not a standard representation. But if you need a moment object out of it, using moment("01012017") will give "Invalid Date" response when formatting. Instead, use moment("01012017","DDMMYYYY")

var d = moment("01012017")
d.toISOString() => "Invalid date"

var d = moment("01012017", "DDMMYYYY")
d.toISOString() => "2016-12-31T18:30:00.000Z"

In your code, when creating 'date' variable pass "hh:mm:ss A" as second parameter in the moment constructor as mentioned below .

   var date = moment(startdate, "hh:mm:ss A")
        .add(seconds, 'seconds')
        .add(minutes, 'minutes')
        .format('LTS');

Moment has really good documentation. I would check it out: http://momentjs.com/docs/

But to address your question more directly, you could do something like:

var secondsToMinutes = '3:20';
var seconds = secondsToMinutes.split(':')[1];
var minutes = secondsToMinutes.split(':')[0];

var momentInTime = moment(...)
                   .add(seconds,'seconds')
                   .add(minutes,'minutes')
                   .format('LT');

You should use the actual handlers to the best of your ability. There are some cool things you can do with durations now, but this is more succinct.

Edit:

As mentioned in a different answer:

 moment('2:00:00 PM', 'h:mm:ss A')

Is necessary if you're handling that format. Regardless - adding/subtracting minutes/hours to a moment object is trivial. Passing invalid strings to a moment object is a different issue in-and-of itself. ;)