Perhaps you could try a "When record enters view" trigger instead?  It seems like the view filters respect timezones so that may work

Thanks for your suggestion, but this is a problem with a conditional step within the automation itself, not the trigger. The trigger is driven by a non-date event. This conditional step, which sends an email, should only happen during certain times. That’s why we have a conditional group at the end of the automation—if we’re within a certain window, only then send an email.

What if you used a formula field to figure out whether it's within the window you want and use the conditonal on that instead? 

I think that would work better, @TheTimeSavingCo. Thank you for the suggestion.