  In quantum mechanics, time is introduced as a non-measurable quantity, as
there is no possibility to build a hermitian operator canonically conjugated to
the Hamiltonian. We cannot have, therefore, the time operator, which means that
the temporal structure of the evolution of quantum systems is ill-defined. We
present an extension to the model, in which the time evolution is based on the
projection postulate rather than the unitary operator. This approach is in
agreement with all other aspects of quantum mechanics and allows to discuss
time as an observable. Using this framework we present a description of the
temporal double-slit experiment in which a~single particle interferes with
itself from a different instant of time. Such behaviour has already been
observed experimentally but lacked a consistent theoretical explanation.
