We discuss the role of finite time and energy uncertainty in the quantum field theory description of neutrino oscillations. In order to to achieve this goal, we review the flavor Fock-space approach and the time-energy uncertainty relation in the Mandelstam--Tamm form, expressed as a flavor-energy uncertainty relation. Such relation, together with the inequivalence of mass and flavor neutrinos Fock spaces, puts a lower bound on neutrino energy uncertainty. Similar considerations can be derived by a perturbative computation of flavor transitions, which employs the Dirac picture to compute flavor transition probability. Remarkably, both flavor Fock space and interaction picture approach lead to the same oscillation probability, within the approximation adopted in the perturbative calculation.