8PM is my favorite if it's raining/snowing. The music box effect really agrees with that song, and it's so pretty.
But on normal days, 1AM. It's probably one of the most calming themes on the entire OST. The music box effect doesn't flatter it as well, sadly, but it's still pretty nonetheless. 11PM is also hella beautiful and tied with 1AM for "Most beautiful" IMO xD
Also, it doesn't count, but there's a special little place in my heart for "Welcome to Our Town." It's the music you hear when you make a new character, before you speak to Isabelle or Tom Nook.
Oh okay, I used to listen to a playlist with Animal Crossing songs to falls asleep to and they called it 2am. I was already a bit confused when I heard the theme starting at 1am last night, so apparently my thought that it started at the time it's called wasn't that weird. It's the 1am theme I like best then indeed.