@Downhill Dino The setup for the time of day changes only works when you enter an actual race, that's why we do it on practice runs in the pre-race menu.
activate the codes, load a race (in my case the Grand Valley Speedway enduro) and then test drive. You don't need to go into qualifications and skip them, just test drive right away with the code on.
Also make sure you bought all the authorized parts (sport brakes, race suspension, triple plate clutch, race flywheel), otherwise you'll be at a disadvantage here.
(the codes are not for cheat engine, they're for a gameshark/action replay/psx emulation cheater)