I would even say that 24 hours probably isn't enough to test it out. Due to the inherent varying nature of Bitcoin, using anything less than a 7 day average is really just an estimate, and probably not a very good one at that.
My numbers come from an average over about 2 days for each, it's a good point that I need to push it out further, thus far it's held for a 48 hour average but I'll stretch it out longer.
To address a post further up, I was wondering the same thing about how the rates are calculated, with any shared pool there is more to one's effeciency than simply raw churn given the frequent fetches, etc.