Yes. Anything above 6 days you do not need to upvote. Having said effective, any range is effective, the only difference is how much VEST can you vote generate. Higher percentage of voting power generate more VEST, better chance to benefit for the person who receive upvote and as a giver would receive a small portion of the curation reward as well. To me 80% and above is good. So I usually won't let my voting power go below that because I am quite active. For people who check back every two days, they can choose to splurge their voting power to 60%. Everyday is 20%. Simple math.