How to quantify simultaneity in quantum measurements?

The prototype for a simultaneous measurement of two conjugate variables was introduced by Arthurs and Kelly in 1965. Nowadays, it serves as a blueprint for a variety of similar setups. Starting from this seminal approach we investigate a refined scheme to measure position and momentum of a free particle. The setup relies on coupling the particle at hand to two ancilla systems, which serve as measurement pointers. By considering explicitly time-dependent interactions we can quantify the simultaneity of the measurement. The question arises, how much information can be obtained in such a measurement setup.