From the idea excellent, unfortunately poor implementation

Positives:
- good idea
- Very good and easy to use User Interface
- Free

Negatives:
- Works unfortunately only three times out of ten, is so unwatchable
- Does not start automatically after turning off the screen, unfortunately, by a simpelen Start button

Alternative app:
- Unfortunately not, in Google Play Sleep Timer is excellent in the Amazon Appstore - not to load on Fire HDX.