This is just a „Warnstreik“ and it lasts for one day. If no headway is going to be made in the talks between union reps and companies, there might come a longer strike until an accord can be found. Last year, nurses and other assistant staff at the six university clinics in Germany’s largest federal state of NRW striked for six weeks.

Just to add: Real strikes could (hopefully not) follow after the 29th, when the last bargaining round ends.