Default Nightmode healthy for battery / display?

So in CM 11 there is this daydream option with a dimmed clock. The background however is not fully off but glowing very lightly. I was thinking of recharging the S4 Mini over night while leaving this mode on.

1. Is this healthy for the battery when it is charged longer than needed over night? Also the nightmode is sucking always a little energy.

2. Is this healthy for the display when the background is always glowing a little. Should I search for an app which is completely dark in the background?

Thanks guys
Tom