Is there a way to change the US date format in Timetracker to the format my country uses?
Timetracker uses the date format in your settings from TFS/VSTS. It is defined in the user's profile: https://app.vsaex.visualstudio.com/me?tab=edit
Changing your settings here should likewise change the formatting in Timetracker for you. Please note that it sometimes takes some time for the changes to take effect, often due to some caching on the VSTS side.