The biggest problem with this project is the 9V battery, any proposed circuit using a 555 timer is going to flatten the battery in a few hours, or a few days if you are lucky.
You can:
- Forget the dimming and just use a switch to turn the light on and off
- Design a circuit that goes to sleep and consumes negligible power when it shuts down
- Use a mains power supply
You might get away with using a large capacitor to keep the LED on after the switch removes the power. You will get the fade and zero power consumption when off. Only problem being that the switch will have to charge the capacitor when it closes and that might flash the contacts.