Adequate Sleep for Zebra Finches?

I have read online that Zebra finches need 10-12 uninterrupted hours sleep a night. We keep ours in an uncovered cage in a room where there are large windows and glass doors, so they wake up at the first sight of daylight, and start singing. In the winter they get close to 10-12 hours sleep, but I am wondering what they need in the summer months, as then they will be waking up between 4 and 5 am, and will get less hours of sleep. Is this a problem? Should they be getting less hours of sleep in the summer or should it be 10-12 hours all the year round?

By P.S.