Estimated change is the estimated change in your balance if the pool found a block at that moment. It is not earned and not locked in until the pool finds a confirmed valid block. The "As of last block" portion is locked in, assuming the last block remains valid.

The estimated change is basically the value of all shares that you have in the top 25 BTC of the pool-wide share log at that moment. This goes down if you lose hash rate, or if the pool gains hash rate (since your relative contributions per block would be less, not that you actually make less overall). It goes up if you add hash rate, or if the pool hash rate goes down.

The last block was pretty long, so likely no change in balance in your time window (not sure on timezone for your times).  All blocks are listed on the stats page with UTC timestamps.

Again, apologies for taking some offense. I get so many people who have been so misinformed about mining that look to blame the pool or me for their ignorance, directly or indirectly.  Your post read a lot like, "my balance changed for no reason, the pool must be cheating me."

I mean, I literally had someone threaten to sue me for the 100 bitcoins that I supposedly owed them for their week of mining at like 50 Gh a couple of months ago.  Seriously.  He was basing his numbers on some outdated profit calculator that some eBay seller linked to that used a difficulty from pre-ASIC days, probably to screw someone that didn't know better (successfully). It was sad, funny, and highly annoying.  And stuff like this happens daily, although not necessarily to that extreme.  At least a dozen times per day I get people wondering why they can't find their stats, or that their stats are wrong, only to find out that they're CPU mining or misunderstood how much they should be earning, or whatever.

I agree that the stats and website need a full overhaul to make some things more clear and better looking overall. But they are correct as they are.  The balance numbers come directly from the reward system and are just parsed and displayed.