You can disable/enable default route by scheduler.
/system scheduler add name="Disable def.route" \
interval=24h on-event="/ip route set disabled=yes \
numbers=\"[ /ip route find dst-address=0.0.0.0/0 ]\"" \
start-time=22:00:00 policy=read,write
/system scheduler add name="Enable def.route" \
interval=24h on-event="/ip route set disabled=no \
numbers=\"[ /ip route find dst-address=0.0.0.0/0 ]\"" \
start-time=08:00:00 policy=read,write
or you can disable/enable WiFi interface
/system scheduler add name="Disable WiFi" \
interval=24h on-event="/interface wireless \
set [ find default-name=wlan1 ] disabled=yes" \
start-time=22:00:00 policy=read,write
/system scheduler add name="Enable WiFi" \
interval=24h on-event="/interface wireless \
set [ find default-name=wlan1 ] disabled=no" \
start-time=08:00:00 policy=read,write