  Here, we report an exhaustive study of the frequency-dependent ac-magnetic
susceptibility of the $D_{2d}$ symmetric Heusler system Mn-Pt(Pd)-Sn that hosts
antiskyrmions over a wide temperature range. Magnetic relaxation studies using
Cole-Cole formalism reveal a Debye-type relaxation with a nearly negligible
distribution in relaxation times. In contrast to the archetypical skyrmion
hosts, the high Curie temperature ($ T_C $) of the present system ensures
shorter switching times, and, correspondingly, higher frequencies are required
to probe the relaxation dynamics. We find a non-monotonic variation in the
characteristic relaxation time with distinct maxima at the phase boundaries
\textit{via} helical $\longrightarrow$ antiskyrmion $\longrightarrow$
field-polarized states, indicating slower magnetization dynamics over the
region of phase coexistence. The temperature-dependent relaxation time across
different phases is of the order of $ 10^{-5} - 10^{-4} $ s and follows the
well-known Arrhenius law with reasonable values of the energy barriers. The
present study concerning the magnetization dynamics in the antiskyrmion host
tetragonal Heusler system is an important contribution towards the basic
understanding of the dynamical aspects of antiskyrmions for their potential
applications.
