https://www.epo.org/en/node/conduct-oral-proceedings-8

Which time zone do we use as standard?

All times we specify, for example in the summons to oral proceedings or vocally during oral proceedings, are local time at our offices in Munich, The Hague and Berlin. 

These locations use Central European Time (CET) i.e. UTC +1, and Central European Summer Time (CEST) i.e. UTC +2. CEST starts on the last Sunday in March and ends on the last Sunday in October.