Secret Place On Pokemon Deluge How Do You Know When Mystery Gift Events Take Place? Pokemon Platinum?

How do you know when Mystery Gift events take place? Pokemon Platinum? - secret place on pokemon deluge

I just found out about Mystery Gift in Pokemon Platinum Rotom, and received the secret key, but how can I know when to get another secret gifts that I? I look forward particularly interested in obtaining the mysterious gift that allows me to meet the legendary Shaymin or Darkrai. If you could give me some information about the date of receipt of this mysterious gifts and I was able to take a site that could help link would be greatly appreciated. Thank you guys. (Or girls)