Looks like this is working:

setResolutionFields();






function setResolutionFields() {


   if (current.resolved_by.nil())


   current.resolved_by = gs.getUserID();


   if (current.resolved_at.nil())


   current.resolved_at = gs.nowDateTime();




   // Update the fields that indicate the time and duration of this incident from open to resolve.


   // Keep track of duration as a glide_duration value (dd hh:mm:ss) and as a pure number of seconds.


   // Both calendar time and business time are maintained.




   var dataChange = current.opened_at.changes() || current.resolved_at.changes();


   var opened = current.opened_at.getDisplayValue();


   var resolved = current.resolved_at.getDisplayValue();




   if (dataChange || current.business_duration.nil()){


   var dur = calcDurationSchedule(current.opened_at, current.resolved_at);


   current.business_duration = dur;


   }




   if (dataChange || current.business_stc.nil())


   current.business_stc = gs.calDateDiff(opened, resolved, true);




   if (dataChange || current.calendar_duration.nil())


   current.calendar_duration = gs.dateDiff(opened, resolved, false);




   if (dataChange || current.calendar_stc.nil())


   current.calendar_stc = gs.dateDiff(opened, resolved, true);


}






function calcDurationSchedule(start, end) {


   // Get the user


   var usr = new GlideRecord('sys_user');


   usr.get(gs.getUserID());


   // Create schedule - pass in the sys_id of your standard work day schedule and pass in the users timezone


   var sched = new GlideSchedule('08fcd0830a0a0b2600079f56b1adb9ae',usr.time_zone);


   // Get duration based on schedule/timezone


   return (sched.duration(start.getGlideObject(), end.getGlideObject()));


}