This is anecdotal, but I've typically fasted in a similar way (eat between 4-8pm only) for around 5 years. A few years ago I was running 20-30km while fasted without issues. I was running slow (5:30 per kilometer) but I felt pretty good, with steady energy and no weakness or crashing. I took a while to adapt to not eating first, but I'd say it was a matter of a month at most.

I personally did (and do) drink a lot of water if I feel hungry. I usually end up hungry the next day if I allow myself to eat past 8 or so - it's always a mistake for me to do that.

I allow myself to have tea and coffee, which some people say isn't true fasting because you have to metabolize the things in the tea or coffee. I don't mind. I'm doing this to maintain control over bad eating habits which lead me to be very overweight. I have ADHD and I suppose it comes with poor impulse control in my case - I tend to be very "all or nothing", so fasting works very well for me. I have nothing until I can have it all :)

I drink at least a liter of water to help keep the feeling of hunger away. I learned that if I keep the meal small preceding the fast I don't struggle during the fasting day. Sometimes even if I follow all these rules I may feel hunger regardless after hour 21.

I'm not the best person to ask about energy levels because I take a medication that depletes my energy so I'm drinking caffeine a lot to stay energized. I can honestly say the last hour is the real challenge after doing it this long.