create script named, for example 'delete':

add name=delete source={/ip firewall mangle remove [/ip firewall angle find]}

create system scheduler task that will run this script each day at 12 o'clock:

system scheduler add name run_del diasabled=no on-event=delete interval=24h start-time=12:00:00

Why not just make rules with a time-of-day criteria, or if possible, (don't know what the mangle rules are doing), make rules that match based on an address-list and you could put timeout on the address-list entries, which would clear themselves automatically whenever the time expires....