  An effective description of microscopic measurements is given, in which the
precise moment of probing is not determined. Within this scenario we propose a
scheme that relies on an "attempt" to make a forbidden simultaneous measurement
of two incompatible observables. Although bound to failure in what concerns
this goal, the process can lead to information on a possible non-vanishing time
scale $\delta t$ involved in the collapsing of the wave function, even if the
duration $\Delta t$ of the individual measurements is much larger than $\delta
t$.
