I don't know how anyone has the time or the mental stress capacity to check their stats daily!
I do mine once per month, just after the end of the month (to see the previously month's results).
Other than that, I might just have a quick glance at a couple during the month if I am logging-in for other reasons.
I voted 6-10. From my point of view it´s important to check some daily. Some changes at ad space given due to current program revenue (negatives) can earn some extra bucks...