How long was guernica bombed?

Germany

I hope this answers your question.

"Guernica, the oldest town of the Basque provinces and the center of their cultural traditions, was almost completely destroyed by the rebels in an air attack yesterday afternoon. The bombing of the undefended town far behind the front line took exactly three quarters of an hour. During this time and without interruption a group of German aircraft -- Junker and Heinkel bombers as well as Heinkel fighters -- dropped bombs weighing up to 500 kilogrammes on the town. At the same time low-flying fighter planes fired machine-guns at the inhabitants who had taken refuge in the fields. The whole of Guernica was in flames in a very short time."

The Times, April 27, 1937.