Once or Twice a day! I mostly check my impressions and clicks and the CTR. I am impatient to know about those.
I check my Adsense account on a daily basis. I think that's enough to see the trending in my clicks and earnings.
I used to see it every hour and then, i love to see the $$ increasing every hour. When i started using it, i hardly earns 1$ a day and now it has increased to around 120$ to 150$ a day, so i hardly put my eye off ..
when i am not so busy, i will see my adsense, i am so busy these days, so , hmmmmm once or twice one day
too many times, checking the adsense you lose money because you spend less time creating content for your website.