According to the management, if there are no customers coming in OR if the restaurant runs out of something important such as French fries or hamburger buns, then the restaurant is closed early.
I remember when I worked for Wendys, part of the year we closed down early since our sales didn't justify staying open later. Another reason may be that the website is showing the average closing time, and closing times may vary from resteraunt to resteraunt, hope this helps
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