Perhaps the cheapest way of reducing the DOC of an aircraft is to operate EMPTY. You could even remove the seats, too !
I lack information on the effect that this would have on the F27. A ball park figure for a B707 was that each extra tonne used 30kg./hour, ie. on a 7 hour flight this one tonne would have used 210 kg. more fuel.
To reduce the total cost, one airline was said to schedule flights to depart Base in the early evening - because otherwise ground staff would have to be paid overtime. Flight crew were not paid extra for night flying !
Can your F27 be operated at night to your destinations ? Night curfews may restrict some operations. Or can reduced landing fees be arranged at times when the traffic would otherwise be slack ? You could increase the profitable utilisation by keeping operating throughout the 24 hours. Passengers may be prepared to travel at 2am for a low enough fare.
Passengers normally return. Freight tends to have a single flight, so a different return load ought to be found, if possible.
Freight can be carried throughout the 24 hours. Not all freight comes under the traditional list of "Urgent, Fragile or Valuable". While a freight door can make turnarounds faster, I carried a lot of 40 gallon oil drums, which had been loaded through an ordinary passenger door, and some garden wheel barrows we carried 3000 nm.!
There is a "Zero Distance Cost" to be considered, somewhere, ie. all those costs without actually moving the aircraft.
LT