Many airlines follow the "flat tire rule," putting you on the next possible flight if you show up within two hours of your original scheduled departure. That wouldn't help you, though.

I agree: best thing to do is be honest and take the outcome.

(I one made a 12-hour mistake, reading AM for PM, and was accommodated - but that was a long time ago, things have tightened up across the industry since, and I had what was then the airline's top status to help.)