After learning that there was no possible way to force my display to sleep when I wanted it to, I thought of the following work around. Copy the following AppleScript into Script Editor (change your_password to your admin user's password) and save it as an Application:
This script will change your display sleep time to 1 minute, wait 90 seconds (during which time, if you've left your computer, the display should sleep), then change it back to 30 minutes. Since it's saved as an application, you can just double-click it to run it. I use this just before going to bed.
do shell script ("pmset dim 1") password "your_password" ¬ with administrator privileges delay 90 do shell script ("pmset dim 30") password "your_password" ¬ with administrator privileges
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