If the message is the internal battery has run dry clock based events will no longer occur etc etc then it's the battery in the game pak.
This question has appeared at least 10 times in the past month.
To fix it, you must replace the battery or take it somewhere to have it replaced.... gamestop, nintendo, etc.
If it says something other than what i listed then it's a bad game (cheating or fake)... either you cheated and are facing the consequences or you bought a fake cartridge.
Bashaamo said:
A friend of mine got the game, and it had that immediately. I'd say that's normal, except maybe there will be no evolutions done by time [Eg. Wurmple evolve into Silcoon in the Day and Cascoon in the Night] but that shouldn't be such an interruption to your game. :/
wurmple does not evolve by time of day... that's a rumour that is not true. Eevee is the only time based evo.
You will only get one of the eeveelutions by friendship and you won't get berries to grow or tv shows.