Google Apps Script can't change timezone in project properties

I can't change the timezone in one of my scripts using File->Properties. I can in my other scripts, they have a dropdown for timezone. Any idea why?

I'm not sure if this will help, but it might be worth a try:

1. In the script editor go to View > Show project manifest.
2. If you are the owner of the script, you should be able to edit the timezone in there.

I have no experience editing that particular parameter as I have never needed to do that. However, I presume that the field is there for the purpose of setting the timezone, so in theory, it should work. You might have to do some experimentation to see if changing it does indeed do what you need. Anyhow, here is the documentation for that file in case you need it:

General manifest documentation

Details of each field

I hope that helps.