I’m not sure they would have done other routes though and certainly not DUB. It’s more likely they would have operated somewhere from SEN inbetween, eg LDY-SEN-XXX-SEN-LDY-SEN-LDY. This would also allow them to swap aircraft and crews.
That schedule would be pointless. How does one travel from London to Derry, then have a full day’s business before flying back to LON?