Toggle Mojave's dark mode automatically based on given time.

launch_task.sh

# NOTES:
# • Don't forget to change every <HOME> in the scripts to your home folder name.
# • Copy .plist and .scpt files into your Library/LaunchAgents folder.
# • First time execution would require permission.
# • Toggle time is hard coded in the script as:
#   – light mode: 07:00-17:00 (day time)
#   – dark  mode: 17:00-07:00 (night time)
# • Execution interval: every 10 minutes (600 seconds).

# load task
$ launchctl load -w /Users/<HOME>/Library/LaunchAgents/local.darkmode.toggle.plist

# unload task
$ launchctl unload /Users/<HOME>/Library/LaunchAgents/local.darkmode.toggle.plist

# check task
$ launchctl list | grep local

local.darkmode.toggle.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
	<dict>
		<key>Label</key>
		<string>local.darkmode.toggle</string>
		<key>ProgramArguments</key>
			<array>
				<string>/usr/bin/osascript</string>
				<string>/Users/<HOME>/Library/LaunchAgents/local.darkmode.toggle.scpt</string>
			</array>
		<key>StartInterval</key>
			<integer>600</integer>
		<key>RunAtLoad</key>
			<true/>
	</dict>
</plist>

local.darkmode.toggle.scpt

-- get seconds since midnight
set ticks to (time of (current date))

tell application "System Events"
	tell appearance preferences
		set dark to dark mode
		-- time > 17:00 or time < 07:00 
		if ticks ≥ 61200 or ticks ≤ 25200 then
			if not dark then
				set dark mode to true
				set appearance to graphite
				set highlight color to graphite
			end if
		else
			if dark then
				set dark mode to false
				set appearance to blue
				set highlight color to blue
			end if
		end if
	end tell
end tell