Had a co-worker get burned by this difference on a last minute trip we had to take with a flight home on AC. He was used to looking for red eyes along with the day before and booked a 12:05 flight from YEG-YYZ.

Got to YEG and the TA said to him "Boy, you should have been here last night!" to which had asked why, did something exciting happen? And she responds "No, that's when your ticket was for!"

Needless to say he was embarrassed and I made sure to give him some grief but the TA rebooked him and only charged him a $75 same day change fee instead of change fee plus fare difference, or worse, making him buy a new ticket outright which she would have been within her rights to do.

But he sure does double check now to make sure his red eye flights are on the right day!