Lighthouse Keeper?

Do you want to win a signed first edition of The Lighthouse Keepers my new Y/A novel? You do? Well, nothing could be simpler, just read on. First, a little background. The book is about a boy from New York who inherits a lighthouse on an island off the County Antrim coast and has lots of adventures there. The island is based on Muck Island near Islandmagee and lovely Kinbane castle (top, right) but the lighthouse is based on the Blackhead Lighthouse in Whitehead, County Antrim. If you look at the LOWEST photograph you'll see Blackhead Light and in the left hand corner of the pic you can just see my sister Diane's house. I used to walk my sister's dog from her house up to the lighthouse and back. This is the competition: What was the average length (in minutes) of those dog walks? Of course every walk was different but the average was remarkably consistent. You could set your watch by it. Two clues: First, Ruffie was an older dog who didnt like to be out too long. Second, the lighthouse is actually closer to the house than it looks from the photograph.
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The THREE closest guesses will get the signed book, lovingly airmailed to their fair city/town/survivalist shack by me own grubby paws. Closing date is midnight Monday 29th Eastern Time, which is 5 am on Tuesday the 30th UK time and 2PM on Tuesday the 30th in Australia. Two rules: one entry per person please and second you have to promise to review me on Amazon. Doesnt have to be a good review, just a review. Fair enough?
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Put your guess in the comment box below and remember to include your email address. If you have a blogger account you can tick the follow up box, otherwise include it in the post. Whew...GOOD LUCK!!!