National Rebound Day works best with night game. There's a much higher concentration of defiant women out in bars the day after Valentine's than anywhere else.
You can still look for them in day game. But given they're a minority of women out and about, you'll need to do a bunch of approaches to find them anything close to reliably.
Nightlife is far and away your best shot.
Unless you do a bunch of approaches during the daytime.
(though you can certainly keep your feelers out during daytime too... it doesn't hurt any. And you will sometimes run into defiant girls by pure chance this way)
The 'holiday' still applies in any country where Valentine's is a big deal. And national character matters somewhat... Western women are more likely to respond with defiance to things they view as slights as women from some other parts of the world are. But yeah, especially in the West, if Valentine's has a lot of cultural significance, the anti-holiday of National Rebound Day is there to pick up the pieces the day after ;)