Chapman - 9:12 pm on Jan 4, 2013 (gmt 0)
Interesting observations, I'm inclined to agree with your analysis. Yesterday, my numbers were good until mid-afternoon and then began to evaporate.
I got very little in the way of clicks or revenue for the rest of the evening and into the night BUT... my early morning (6:30 AM) revenue today was almost half of a typical completed day! Never saw that before.
The day continued with amazing CTR and EPC until about two hours ago and then it was a repeat of yesterday.
Like you, my most active visitor periods are in the afternoon and evening as my sites cater to educators, children and their parents so this makes almost no sense at all.