Eurogamer reports. This means the four-hour window from 11 p.m. to 3 a.m. is the only time during which games like Assassin's Creed 3 or ZombiU can be purchased, or even have their trailers viewed.
We've checked with a fictional panel of experts, and the general consensus is that this a totally weird thing for a company to do, especially considering that the Wii U already has parental controls implemented in its operating system. The block appears to apply to all accounts and it's uncertain whether it's possible to opt out of the restriction in any way.
What we do know: if we were given a Wii U but had to wait until just before midnight to download the game we wanted, we'd just go to the damn store and buy it. We've reached out to Nintendo of Europe and Nintendo of America for more information; perhaps there's some other logic at play here that isn't apparent.
Update: Nintendo of America tells Joystiq "This is a European policy and does not impact Nintendo of America."