Why is the Runtime attribute 0 in Gurobi 9.0 (or earlier)?

This is only relevant for Gurobi 9.0 and earlier versions. This issue has been fixed in Gurobi 9.1.

Sometimes the Runtime attribute incorrectly returns 0 after optimizing. This is due to a known issue with calling model.update() or model.write() before querying the Runtime attribute.

To obtain the correct runtime, please query the Runtime attribute immediately after the model.optimize() call.