You won't pick up business traffic with just an evening rotation. There has to be at least a morning one as well. You can get away with one rotation if there is no direct competition, but with Ryanair and Aer Lingus both offering multiple daily services to London, it wouldn't be enough.
Agreed on the comment re flight times. A 16:00 departure ex Cork and a 17:55 ex LCY are too early for last flights if you want to pick up business traffic. You need to let people get as close to a day's work as possible.