Maybe I missed something. I'm at the "Clear Supernova once" growth event mission, having just gotten a key to clear the previous mission, but I can't seem to enter the supernova mode. The "Battle" button is greyed out. Do you need all 5 keys or somesuch? There's also text saying "Reset Power 23 hour 32 min remaining". I did enter it once for the little tutorial fake fight, but that was over 30 minutes ago, so I don't think it's a case of a 24 hour lockout?