Enable "Dark Mode" at 6:30pm daily using this Windows Task Scheduler XML file

Dark_Mode_Enable.xml

<?xml version="1.0" encoding="UTF-16"?>
<Task version="1.2" xmlns="http://schemas.microsoft.com/windows/2004/02/mit/task">
  <RegistrationInfo>
    <Date>2022-10-23T19:30:00.0000000</Date>
    <Author>SCI\SpiralChaotic</Author>
    <URI>\SCI\DarkModeEnable</URI>
  </RegistrationInfo>
  <Triggers>
    <CalendarTrigger>
      <StartBoundary>2022-10-23T18:30:00</StartBoundary>
      <Enabled>true</Enabled>
      <ScheduleByDay>
        <DaysInterval>1</DaysInterval>
      </ScheduleByDay>
    </CalendarTrigger>
  </Triggers>
  <Principals>
    <Principal id="Author">
      <UserId>%ComputerName%\%Username%</UserId>
      <LogonType>S4U</LogonType>
      <RunLevel>LeastPrivilege</RunLevel>
    </Principal>
  </Principals>
  <Settings>
    <MultipleInstancesPolicy>IgnoreNew</MultipleInstancesPolicy>
    <DisallowStartIfOnBatteries>false</DisallowStartIfOnBatteries>
    <StopIfGoingOnBatteries>true</StopIfGoingOnBatteries>
    <AllowHardTerminate>true</AllowHardTerminate>
    <StartWhenAvailable>true</StartWhenAvailable>
    <RunOnlyIfNetworkAvailable>false</RunOnlyIfNetworkAvailable>
    <IdleSettings>
      <StopOnIdleEnd>true</StopOnIdleEnd>
      <RestartOnIdle>false</RestartOnIdle>
    </IdleSettings>
    <AllowStartOnDemand>true</AllowStartOnDemand>
    <Enabled>true</Enabled>
    <Hidden>false</Hidden>
    <RunOnlyIfIdle>false</RunOnlyIfIdle>
    <WakeToRun>false</WakeToRun>
    <ExecutionTimeLimit>PT1H</ExecutionTimeLimit>
    <Priority>7</Priority>
    <RestartOnFailure>
      <Interval>PT1M</Interval>
      <Count>3</Count>
    </RestartOnFailure>
  </Settings>
  <Actions Context="Author">
    <Exec>
      <Command>%SystemRoot%\system32\WindowsPowerShell\v1.0\powershell.exe</Command>
      <Arguments>-NoProfile -NonInteractive -ExecutionPolicy Unrestricted $RegPath = 'HKCU:\SOFTWARE\Microsoft\Windows\CurrentVersion\Themes\Personalize'; New-ItemProperty -Path $RegPath -Name SystemUsesLightTheme -Value 0 -Type Dword -Force; New-ItemProperty -Path $RegPath -Name AppsUseLightTheme -Value 0 -Type Dword -Force</Arguments>
    </Exec>
  </Actions>
</Task>

Almost 100% based on this Windows Central article.

I changed powershell.exe's command switches to include -NoProfile, -NonInteractive, and -ExecutionPolicy Unrestricted.
For semantic purposes, I slightly changed the PowerShell code so that it reads as follows:

$RegPath = 'HKCU:\SOFTWARE\Microsoft\Windows\CurrentVersion\Themes\Personalize'
New-ItemProperty -Path $RegPath -Name SystemUsesLightTheme -Value 0 -Type Dword -Force
New-ItemProperty -Path $RegPath -Name AppsUseLightTheme -Value 0 -Type Dword -Force

I also made some adjustments to the task's "Conditions" and "Settings" tabs.

Usage via Task Scheduler:

1. Save the file from this gist to your computer
2. Open Task Scheduler (taskschd.msc)
3. Choose a Task Scheduler Library from the pane on the left
4. Right-click any whitespace in the main pain, then click "Import Task..."
5. Navigate to the location where you saved the .xml file, select it, then click "Open"
6. A "Create Task" dialog will appear, pre-populated with the values from the .xml file
7. Click the "Change User or Group..." button
8. Enter your Windows username, then press enter (or click "OK")
9. Click "OK" to close the dialog; the task has been imported

To test the task, ensure your computer isn't already using this mode, then right-click the task and click "Run." The change should occur almost immediately. Return to Task Schedule and refresh the window by pressing F5. The "Last Run Result" column should state, "The operation completed successfully. (0x0)."

To change the schedule, double click the task to edit it, choose the "Triggers" tab, then click "Edit..." Follow the prompts to make your desired changes.

Bonus note:
If you'd like to skip steps 7 and 8 above, simply edit line 19 in the XML file using your favorite text editor, replacing "%ComputerName%\%Username%" with your username, e.g. "Nevember."
(In most cases you don't need to include the computer name or a domain name.)

Also check out this gist's partner, Light_Mode_Enable.xml, which I recommend using in conjunction with this one.