Yes this option ("Use timezone from locale") is valid for the operating system timestamps, but no for the pdf attributes, those are still inexact.
It's similar for Spain. The access and modification times are setting to 02:00:00 CEST which is the UTC mark for peninsular Spanish time, but for example, just now are 18:03 and if I create a PDF with gscan2pdf the access and modification times are however setting to 02:00:00 CEST.