# Time-dependent quantum mechanical picture

As we know,there are three kinds of pictures in quantum mechanics, namely the Schrodinger picture, Heisenberg Picture and also the Dirac picture. If you look at the Wikipedia about the explanation of Schrodinger picture, you will find in which it tells you that the observables in Schrodinger picture are constant with respect to time.

But in fact we will meet some questions in which the Hamiltonian is exactly time-dependent? And the evolution operator will be $$U(t) = T\exp{\left(-\dfrac{i}{\hbar}\int_0^t d t' H(t')\right)}.$$ What's the paradox in there ?I am confused with this.