  Deffner and Lutz [J. Phys. A 46, 335302 (2013) and Phys. Rev. Lett. 111,
010402 (2013).] extended the Mandelstam-Tamm bound and the Margolus-Levitin
bound to time-dependent and non-Markovian systems, respectively. Although the
derivation of the Mandelstam-Tamm bound is correct, we point out that thier
analysis of the Margolus-Levitin bound is incorrect. The Margolus-Levitin bound
has not yet been established in time-dependent quantum systems, except for the
adiabatic case.
