The first Bayreuth Ring cycle was supposed to be from 13 to 16 august 1876, but due to indisposition of Franz Betz (Wotan/Wanderer) Siegfried and Gotterdammerung had to be postponed one day. Hence: 13/8 Rheingold 14/8 Walkure 16/8 Siegfried 17/8 Gotterdammerung. The other two cycles went as planned on four consecutive days. (source: Martin Gregor-Dellin - Richard Wagner).
A small addition to the last part of the text:
The first Bayreuth Ring cycle was supposed to be from 13 to 16 august 1876, but due to indisposition of Franz Betz (Wotan/Wanderer) Siegfried and Gotterdammerung had to be postponed one day. Hence: 13/8 Rheingold 14/8 Walkure 16/8 Siegfried 17/8 Gotterdammerung. The other two cycles went as planned on four consecutive days. (source: Martin Gregor-Dellin - Richard Wagner).