Quantum transient currents are obtained after the sudden release of a particle initially confined in a nanoscopic circuit. We extend the 1D theory of diffraction in time to particles released from nanoscopic circuits with cylindrical cross‐sections. For a circular cross‐section, the particle’s free time evolution is described by cylindrical waves with their amplitudes showing diffraction in time. For large observation distances, the time‐dependent probability density current looks similar to the Fraunhofer diffraction pattern by a circular aperture. A temporal quantum Airy disk can be defined.