Answers for "calculate number seconds moment js"

moment calculate duration

moment
 .duration(moment(endTime, 'YYYY/MM/DD HH:mm')
 .diff(moment(startTime, 'YYYY/MM/DD HH:mm'))
 ).asHours()

momentjs date and time string add minutes

moment(date, "DD-MM-YYYY hh:mm:ss")
                        .add(10, 'minutes')
                        .format('DD/MM/YYYY hh:mm:ss');