The maintenace should not effect your income at all. Read the site it says that through the downtime your ads will run, your revenue you will stay up. My revenue went down yestorday too but about 15% but maybe everyone was watching soccer . Not sure but just going by what the site said.
I'm seeing about a 10% decrease today. Could be because of the weekend. Why don't you check your site and compare it to last weekend and see if there was a drop again? That could be a thing. In my situation I've gotten about 600 more unique users with about 10k more pageloads but still 10% decrease in adsense revenue. Different users different days. You can't always expect to make that amount.