when connecting to TFS, you need to specify the ConnectionAdvisor. When no connection advisor is specified when creating a new instance of TFSTeamProjectCollection, a DefaultConnectionAdvisor is created with a default locale and time zone. Maybe it's not setting the default locale and time zone.
However, it's best to set the timezone in the defaultConnectionAdvisor.
ConnectionAdvisor connectionAdvisor = new DefaultConnectionAdvisor(Locale.US, TimeZone.getTimeZone("UTC"));
tpc = new TFSTeamProjectCollection(URIUtils.newURI(TFS_COLLECTION_URL), credentials, connectionAdvisor);
Hope this helps.