I once almost missed a flight home from a holiday due to something like this. Something to do with a 12 hour clock as I recall - so we thought we were leaving the next day, but it was actually early in the morning that day. That probably doesn't make too much sense, but anyway, had my friend not by chance looked at the flight schedule, we'd have missed it.
I check schedules more clearly now.
Oh, yes. Check those schedules!

The first time I booked a plane trip on line . . . bags were packed, everybody was ready to go on an early flight the next morning.
I decided to check the schedule the night before . . . I could not find my flight number. Anywhere. There weren't any flights taking off at my scheduled time either. I had my confirmation that I checked, double checked. No luck.
I called the airline and asked "What gives?" (much more politely than that, I assure you.

)
Customer service was confused, too, because she couldn't find me listed as a passenger on any flights leaving the next day.
I said "But my confirmation says the 18th, that's tomorrow right?" She agreed "Yup. Tomorrow's the 18th.)
She did some magical checking then came back to me and said "I see what the problem is. You have a flight booked for February 18th."
I said "Oh! I'm so glad you found me! So I'm good to go tomorrow?"
CS was sooo gentle and kind to me. I don't remember her exact words when she apologetically informed me that tomorrow was
January 18th. Not
February 18th.
Apparently I was in the wrong month when I booked my flight.

I did write an extremely complimentary letter about her customer service because she was able to get me and the DDs on a flight the next day without extra charges.
(I think she felt sorry for the poor idiot that she was dealing with.)