2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/150926A self-adjoint operator with dimensions of time is explicitly constructed, and it is shown that its complete and orthonormal set of eigenstates can be used to define consistently a probability distribution of the time of arrival at a spatial point.25 pages, LaTeX, no figures. A very minor correction to textQuantum Physicstext