According to Official Guinness Records,
The fastest time to travel to all the Berlin U-Bahn metro stations is 6 hours, 53 minutes and 24 seconds and was achieved by Adham Fisher (UK) in Berlin, Germany, on 26 May 2017. Adham already holds two records of this category and wanted to attempt another.
For a complete list of 2017 records, please visit 2017 Guinness Records in Germany.