Think they’d rather sacrifice the evening departures to ensure the next day/s are unaffected. They did the very same one evening about 6 1/2 years ago when there were about 2 snowflakes on the runway at STN... I can see the logic behind it, not having crew and aircraft displaced, and playing catch up for the next few days etc. But not very fair on the pax of course... but that’s what you get if you’re only willing to pay £50 for a return trip to Spain!