  We discuss the possibility of extracting energy from a single thermal bath
using microcanonical Szil\'ard engines operating in finite time. This extends
previous works on the topic which are restricted to the quasistatic regime. The
feedback protocol is implemented based on linear response predictions of the
excess work. It is claimed that the underlying mechanism leading to energy
extraction does not violate Liouville's theorem and preserves ergodicity
throughout the cycle. We illustrate our results with several examples including
an exactly solvable model.
