Here's a real life example from my friend's router. He's blocking his daughter's phone from the internet according to the day and time in the comments below.
Here it's blocking by MAC address but that's easily changed to IP address or your subnet.
Current time when I copied this is Friday so none of the rules are active hence the "# inactive time" which displays as red colour in Winbox. She's allowed to use the internet whole of Friday.
# inactive time
add action=drop chain=forward comment="Block 0000 to 1830. Mon-Thu" src-mac-address=AC:38:70:14:B4:50 \
time=0s-18h30m,mon,tue,wed,thu
# inactive time
add action=drop chain=forward comment="Block 0000 to 0700. Sunday" src-mac-address=AC:38:70:14:B4:50 \
time=0s-7h,sun
# inactive time
add action=drop chain=forward comment="Block 2100 to 2230. Mon-Thu, Sun" src-mac-address=AC:38:70:14:B4:50 \
time=21h-22h30m,sun,mon,tue,wed,thu
# inactive time
add action=drop chain=forward comment="Block 2300 to 0000. Mon-Thu, Sun" src-mac-address=AC:38:70:14:B4:50 \
time=23h-23h59m59s,sun,mon,tue,wed,thu