Damn...I'd say the best time to join a game in Grepolis is the start of a brand new world, at least everyone starts more or less equal, but like T11 the 'Gold Coin' buyers have a big advantage. A Gold Coin buyer in Grepolis is basically the equilivent of T11's scout buyers.
I've got 1250 points on my city and the leader has over 1700 on Nicaea, looking at my building with not using gold coins and always starting a new construction after a construction has finished, It looks like there are a good number of players who have used gold coins to speed up constructions.