Take LBA as the example. 4 737-300 departures today and 9 737-800 first thing. That's a total of 2293 passengers so let's assume 2293 bags. If they can capture only 10% of those passengers is 230 bags and 230 passengers less to process at check in first thing. A simple increase to 12% and suddenly 275 bags and 275 less passengers.
Jet2 will have the data on hand to know what flights this works on and what flights it doesn't. For example I would imagine they get a greater % using twilight check in for the earlier morning flights (before 7) than those who are flying at 830/9am.