dear all .
i have problem with mikrotik usermanager in rb751 .
i have group with limitation 2hour and after 2 hour , pppoe connection will be disconnected and after that i need
time interval for renew the account in night , for use the connection tomorrow .
please help
thanks all 
first you need to add the function “radius incoming” (coa) so your usermanager actuly can disconnect the user after its amount of time or usage.
then add a script that runs every night with the command “/tool user-manager user reset-counters username” and the user account should be all right to use again.