So yesterday evening I thought I'd finally get into Litecoin mining, since I had a 6950 and never use for anything intensive I'd put it to good use.
I looked online, joined a pool (http://ltc.kattare.com), downloaded the "Reaper" GPU miner, configured it and let it run.
When it was time for me to go to sleep I checked up my account online and it said that I had an estimate of Ł0.0122~, I figured good enough and shut down my computer and went to bed.

When I woke up this morning I realized that the value lowered: it went from 0.01 to 0.009~. I don't get it, could the "estimate" have that much off? This pool functions with PPLNS, and if I understood it correctly it shouldn't affect what I already have mined for should it?

I used the search function but I can't find a thread of where something like this might've happened.
An explanation would be greatly appreciated.

Thanks.