How to compute total time from two separated object keys in Vue js?

Question

I'm expecting to compute total time by subtracting date and time from separated object keys in the data array. Hense I'm having a static start and end date format 'yy-mm-dd' and time format '01:02:30'. And I need to compute its time difference. But I'm not sure if the syntax is ok.

data (
  return {
  shifts: [
    {
      id: '1',
      start_date: '2022-04-23',
      start_time: '19:32:00',
      end_date: '2022-05-23',
      end_time: '07:32:00'
    },
    {
      id: '2',
      start_date: '2022-04-23',
      start_time: '19:32:00',
      end_date: '2022-05-23',
      end_time: '07:32:00'
    }
    ]
  }
)

computed: {
totalShiftTime () {
    return this.shifts.forEach(t => (t.end_date + t.start_time) - (t.end_date + t.start_time))
    // expecting to return smth like 11:12:32 format // means total time
    }
}