If your screen is on at the designated time, dark mode will not turn . The screen must be off. So, if you are using it at 8 pm it won't turn on till you you put the phone down and the screen times out. If you are using it and want dark mode, you can always turn it on manually. There's a quick panel icon for it.
I do not know as I don't use battery saver or power saving. I think it could be a possibility.
There is no need for power saver to be on unless you have less than 20% battery remaining and know you cannot get to a charger for awhile. It actually does not do much to save power when you have a full battery, except interfere with apps you want to use.
Think about it, you are starting your day with 20% less battery. I always have charged all my phones to 100%. I, personally, have noticed no negative impact on battery life. By the time most batteries deteriorate to a problematic extent, one is usually on to a new device anyway. Modern phones stop the charging process when the battery level reaches 100% anyway, so it's not likely to overcharge. If you want, the better option for battery protection would be to choose adaptive battery protection, which will charge your battery to 80% while you sleep and push it to 100% just before your set wake up time.
When you say you are almost at 0% at the end of the day, it also depends on how long your day is from the time you take it off the charger to the time you notice that you are almost empty. You should not let the battery get that low anyway. Do you ignore the "battery low" warning that comes on at 12%?
