you can manually change your computer's date and time and the game will recognize this when you launch it. Just make sure you change the time first before launching the game. Then just remember to re-sync your computer's clock or set the time back to the correct time once you're finished.
When choosing the psychic-type gym, there is someone with a dark type pokemon in the first area. My only damaging move is psychic-type move so I can't progress without losing or running through PP and struggling!