  Nowadays High Energy Physics experiments can accumulate unprecedented
statistics of heavy flavour decays that allows to apply new methods, based on
the study of very rare phenomena, which used to be just desperate. In this
paper we propose a new method to measure composition of $K^0$-$\overline{K}^0$,
produced in a decay of heavy hadrons. This composition contains important
information, in particular about weak and strong phases between amplitudes of
the produced $K^0$ and $\overline{K}^0$. We consider possibility to measure
these parameters with time-dependent $K^0 \to \pi^+ \pi^-$ analysis. Due to
$CP$-violation in kaon mixing time-dependent decay rates of $K^0$ and
$\overline{K}^0$ differ, and the initial amplitudes revealed in the
$CP$-violating decay pattern. In particular we consider cases of charmed
hadrons decays: $D^+ \to K^0 \pi^+$, $D_s^+ \to K^0 K^+$, $\Lambda_c \to p K^0$
and with some assumptions $D^0 \to K^0 \pi^0$. This can be used to test the sum
rule for charmed mesons and to obtain input for the full constraint of the two
body amplitudes of $D$-mesons.
