LOL. This is absolutely NOT a dumb question. The way the timers work in the etron is not straightforward and is poorly documented. Firstly, you CANNOT set a timer based upon the time you want the charging to START. You set the timer by inputting your desired DEPARTURE TIME. For example, if you set the timer to 12am, the car will start to charge so that charging is COMPLETED by 12am.
Secondly, once you have set up a timer, to use it you must first enable it from the MMI shutdown screen. Let's say you have a timer set up the way you want using the MyAudi app. If that is a timer you want to use sometime, then you need to "activate" it in the app with the slider. However, this DOES NOT "enable" the timer to actually work. It only tells your car that this is a timer you might want to use sometime. After that, with the etron running, when you turn off the car a "shutdown screen" appears. On that screen, you will see that "activated" timer option appearing. You need to press the icon by that timer so that a red bar appears above the icon. That will enable the timer. Now, when you get out of the car and plug in the charging cable, the light will slowly pulse white a few times while it is negotiating with the car and then it will start to rapidly blink green, indicating it is waiting for the timer. Now the car will wait until it estimates it needs to start charging so that it will be finished by Departure Time.
You have the option to also "condition (heat/cool) the cabin" as part of the timer set up. If you select that, then about 20 minutes before the Departure Time, the car will begin to condition the cabin, while periodically pulling more current from the wall to replenish the battery. So, in the end, when you head out you have a Conditioned Cabin AND a fully charged battery.