The Chatham Islands are 45 minutes ahead of New Zealand Standard Time, which makes them GMT +12:45 (Just why it's 45 minutes and not a "round" number is a mystery to me).  The Chatham Islands also observe the same daylight saving dates as New Zealand, making them GMT +13:45 over summer months.

Sunrise and set times for both sun and moon at the Chatham Islands can be found on date and time.com