Saved variables are written to file at the end of a session - so at reload or logout. (Just an FYI, if your client crashes then saved variables will not be written.)
(Another FYI...) For a simple addon with simple saved variables, AceDB is overkill and it's TONS easier to just use the built in system. AceDB was written to handle profiles. Some authors still prefer to create their own profile system rather than use AceDB, though this isn't because there's anything wrong with it - just that it's not necessary to use unless you want to.
All that said, AceDB does not save any data if it is unchanged from the default values.
Give this a look over:
https://wow.gamepedia.com/Saving_var..._game_sessions