unless your modem is a modem/router combo, you cant block a user at the modem level because you only connect to the modem via an ethernet cable
most times, you connect your router to the modem and everyone connects to the router. you can block devices connected to a router without affecting others connected to the rsame outer
if your internet device is a modem/router combo (if it was supplied by your ISP, its most likely a modem/router combo) you can access the router interface of the device and set a schedule or block devices outrightly
