A geometric construction of the arrival time in conventional quantum mechanics is presented. It is based on a careful mathematical analysis of different quantization procedures for classical observables as functions of positions and momenta. A class of observables is selected which possess a unique (if any) quantized version. A simple criterion for existence of such a quantized version is formulated. These mathematical results are then applied to the classical ``arrival time'' observable. Physically, the resulting "Quantum arrival time" is identical with the one published in my ROMP (1974) paper, but the proof is much simpler and elegant. Moreover, the uniqueness of this procedure is proved.