I have Adsense Notifier on Firefox so I log in every time I open my browser... and that is every 5 minutes... or less
The minimum of FF notifier is 20m, I log-in once a day, sometimes I don't, I log in to get codes ..... I mean getting money from adsense is not a goal, it's something to help me develope a better website for people, and me .....
I use the FF Adsense Notifier set to 20 minutes, but inbetween I somtimes log in with Internet Explorer, which updates on a different 'track', so i get updates every 10 min or so this way. If i'm at work during the week I may only log in a few times a day - but in the evening it's several times an hour.. i guess i'm a bit obsessive..
Don't we all wish that by checking more often, we would generate more revenue? But it doesn't, so I probably only check twice a day.
It usually depends how busy I am at that day. If I find myself bored, I usually check my earnings. However, if the earnings are depressive I might not check them as often. It kills the day.
I check mine two or three times a day. I think it's important to check in case anything odd has happened like a sudden rise in the the number of clicks or page impressions. If you haven't bothered to check then the first you'll know about it is when you get an email from google.
I rarely check my stats. I usually just go on my adsense page to see how much money I am up to for that month and see if I've reached the payout minimum
The problem with adsense is that it becomes extremely addictive. It does not matter whether you earn much, but checking on the account frequently becomes a habit when you are on the computer.