During discussion with friend I realized that I used to have time of founds histogram in statistics, when I used to generate my statistics using GeoGet.
I know that there is a problem, that not everybody is putting found time in log, but even if I don't have it in all the caches, I am holding the custom putting the time into log, so parsing timestamp should be quite easy. Also generating one more histogram in stats. And since not everybody has this times, it could be hidden as default or so ...
As I browse now through the statistics, there are also some tables Times X Days in week which looks nice, but for the start it would be enough to have just histogram for each hour number of caches.