Playing hours only apply to fast turn-based games.
If you are looking for a turn-based game from the game page, and have the game speed set to a slow turn-based option but also have "flexible" enabled, playing hours won't be visible as an option at all (that only shows up when you've selected fast turn-based), and you can be dropped into a turn-based game of any speed with any playing hours. If you've set a fast turn-based speed, there's an additional setting for playing hours, but if you mark that "flexible" you can again be dropped in to a game with any playing hours. (IMO this UI is terrible.)
For turn-based games that aren't prearranged I suggest using the "play now" lobby. If you're using automatic matching there, under the gear menu you can set specific ranges of acceptable speeds and playing hours, including four levels of preference for the matchmaking system to use if it's taking a long time to find you a game. Alas, you have to set these separately for every game, but they are retained per-game until you explicitly reset them.
There are a bunch of bug & suggestion reports filed complaining about how fast turn-based games are created, described, or marked, and how people think it could be improved. Searching
https://boardgamearena.com/bugs for BGA website and "fast turn-based" will get you many of them.
(Possibly it's worth starting a discussion thread comparing the various suggestions.)