Google engineers will be performing routine site maintenance from 10am to 2pm PDT on Google AdSense servers. During the maintenance you will not be able to log in to your AdSense account. Google will continue serving ads to your pages and tracking your clicks, impressions, and earnings as usual. In addition, your ad targeting won't be affected.
Here are some time converted to different localities.
London - 5pm Saturday
Alexandria - 8pm Saturday
Hyderabad - 10:30pm Saturday
Jakarta - 12am Sunday
Perth - 1am Sunday
This Inside AdSense post has more information about these maintenance sessions, Sphere: Related Content