Timesheet

Hi, I am very new to calculating the fields in an Adobe DC document that takes a time of arrival and departure plus a field for total breaks.

I have found this script:

function getTimeInterval(startTimeMon, endTimeMon, lunchTimeMon){
var start = moment(startTimeMon, "HH:MM");
var end = moment(endTimeMon, "HH:MM");
var minutes = end.diff(start, 'minutes');
var interval = moment().hour(0).minute(minutes);
interval.subtract(lunchTimeMon, 'minutes');
return interval.format("HH:MM");
}

but it doesn't display any results in the total hours worked field.

I need to do this for a two week period and then calculate the total hours for all days worked.

 realise that I will need to add to the script, but i don't want to over complicate things to start with.

Any help would be appreciated, please.

Many thanks