Hi, I was having a similar issue, but found a fix.
I originally set up Working Hours when I was on Mountain Time. Then I noticed that when on Central European Time, Working Hours was still using Mountain Time even though the system clock was set to Central European (Summer) Time. The system sets the time zone automatically based on location.
To fix the issue, I simply set the clock manually in System Preferences, and then quite and relaunched Working Hours. It all realigned itself. The time zone is correct in Working Hours.
Now they're may be an easier solution (quite and relaunch Working Hours). I believe I may have already done this, but I'm not sure.
Anyway hope this helps.