Javascript: how to add n minutes to unix timestamp

Question

I have a unix timestamp: 1368435600. And a duration in minutes: 75 for example.

Using javascript I need to:

1. Convert the timestamp to a string format hours:mins (09:00)
2. Add n minutes to the timestamp: timestamp + 75mins

I tried the moment.js library:

end_time = moment(start_time).add('m', booking_service_duration);

booking_service_duration was 75 but it added an hour. I'd also rather not have to use another js library

Answer 1

Unix time is the number of seconds that have elapsed since 1 January 1970 UTC.
To move that time forward you simply add the number of seconds.

So once you have the minutes, the new timestamp is oldTime + 60*minutes
For the conversion look up parsing libraries, there is code out there for this, do some research.

Answer 2

To add 75 minutes, just multiply by 60 to get the number of seconds, and add that to the timestamp:

timestamp += 75 * 60

To convert to hours:mins you will have to do a bit more math:

var hours = Math.floor(timestamp/60/60),
    mins = Math.floor((timestamp - hours * 60 * 60) / 60),
    output = hours%24+":"+mins;