AC does this sometimes. Once a year or so, they take the late flight into YZF that in summer sits at 9 or 10pm and move it up to 6 or 7pm. Which is great, except now you have to leave eastern Canada by 3pm at latest instead of 6pm which leads to an unproductive day. And, when coming in from TPAC flights, the early schedule would make you miss the last connection so you'd be overnighting. Especially frustrating as the plane sits on the ground overnight...

I emailed once about it since I'd talked to a bunch of colleagues and a bunch of them were flying other airlines instead, or not taking trips, and I was assured route planning were professionals that knew much better than me so I shouldn't worry my pretty little head about it.