When running a scheduled event, you can just run a microflow, as it is performed on the server side (where you store your application) and not client side (mobile phone of the user).
I am not sure if you will be able to log-out all users at the end of the day from the server side, but you can always try.
Perhaps by creating a boolean attribute called LoggedIn that is linked to their account, which is set to TRUE when they log in and which you can use to find logged in users
Other route might be to check for active sessions at the end of the day.