Alrightee, you need to communicate the idea that what we're about to see happened yesterday, in a not uncomedic way. You can't use the word "yesterday" on screen. What would you do?!?
(Yeah alright, I'm fishing for ideas... I fess up. But I'm also interested in exploring all the options available to me. Right now I have a few wipes and a cheesy pond dissolve with some whimsical SFX... They all work, but I want to do better that that.)
I would fix this in the script first, if I had the chance. Tell the story in reverse order, with the horrible thing/consequence (whatever that is) happening first, and someone, the protagonist or someone else, saying "how could this have happened?". Then you cut to the obvious earlier scene. Subtle hints in the setup can be based on the clothing worn and it's condition (Beginning of the day everybody is dressed nice and unwrinkled, end of day jackets and ties are gone, sleeves rolled back, wrinkles, sweatstains, etc.) and the condition and lighting of the set, plus sound effects that hint at the time frame.
Assuming you already have finished footage and no way to go back, clock wipes, a hyper-speed reverse time-lapse exterior of the sun going by, a hand with remote popping in to the lower third and manually rewinding the day like it's a tape on shuttle, are common techniques. Heck, there's a new theatrical movie about to release with THAT premise. You can do the "Groundhog day" shot of the closeup of the morning alarm clock as well.
Great stuff, thanks Mark. I actually managed to use a blow to the head to trigger the flashback. Worked well, and when she "came too" and we come back to present, it's all the funnier as she's been standing there for a while...