I'm making a map where players explore the map during a "day" time and defend against waves of enemies attack during the "night" time.

I don't know how to execute this well. I've tried switches and then tried using units to label day and night and removing them after the count down but I can't get it to work well. Looking for ideas to make this system work.

plenty of ways, the simplest would probably be a timer.

if "day" is cleared
if "night" is set
if timer is at most 0 sec
--
set timer to 5:00
clear "night"
set "day"
preserve

if "day" is set
if "night" is cleared
if timer is at most 0 sec
--
set timer to 5:00
clear "day"
set "night"
preserve

etc etc.

What you can do is have a unit travel from one point to another to signify day/night.