As I understand, row owners don’t directly help for timezones. It is just a security method to let users ownly download rows that “belong” to them.
So the points Jeff suggested, if you don’t want to enable row owners, should go like this:
- Find a way to have the timezone offset of each user in the user profiles.
- Create a template with the signed-in user’s email in the Shifts sheet.
- Create a relation matching that template with the user’s email column in the Profiles sheet.
- Take back the timezone via a lookup.
- Use a math column to calculate the specific timezone for each signed in user.