Just curious to what time your earnings begin to come through, myself I would say it's around 4pm + (GMT), I assume the most of my traffic to my sites are from the US. I get the odd impression throughout the daytime but only 1 or 2 clicks until I leave work then over the UK evening it seems to go up gradually.
I need to get some sites targetting UK traffic, it gets disheartening when you check your adsense and it still shows $0 I may aswell just check yesterdays performance when I wake up then leave it.
I tend to get most of mine after 5pm so I am guessing its an American audience. I discovered it one night when I checked it at 11pm gmt then woke up and noticed a 100 odd more views. I now do a post at 11pm before going to bed and that has boosted my traffic. I love the U.S.A
Clever thinking I'm trying to get a mixture of .com's and .co.uk's so that it's spread out throughout the day. That's the plan anyway