The Time Zone you've setup on your Formstack profile page will determine the timestamps in the document history for documents that are routed for signature as shown below.
To set or adjust the time zone for your location, log in to https://admin.formstack.com/login, go to the Profile tab, and then Time Zone.
Please note: If you see options in this screenshot that are not in your account it could be because of your user permissions or account type. If you have any additional questions about those specific options, please feel free to reach out to support@formstack.com.