AFAIK, your estimated earnings are calculated from the 3hr hashrate. If you've been offline for a while, that rate drops and takes 3 hours to creep back up again... that's why the projected earnings were so low and slowly increased as you were mining for longer.
I was already back for almost 2 days and my estimate was .004 then just dropped off for no apparent reason. If it's based off the 3 hour rate than I should have seen no drop. You can look at the graph at the time when I first posted. My 3 hour hashrate didn't fluctuate at all. Why did my estimate?