This is a review article on the status of the research by summer of 2017. I copy the conclusions:
In the present article we have reviewed current state of
the art of investigations of time crystals originally pro-
posed by Wilczek (Wilczek, 2012), i.e. the phenomena
that are related to self-organization of quantum many-
body systems in time. This kind of self-organization is a
truly quantum effect and should be distinguished from
classical self-organization phenomena where non-linear
oscillators synchronize their motion if a coupling between
them is sufficiently strong . The formation of time crystals is quite
analogous to the formation of space crystals.
While the original time crystal proposition turned out
to be impossible for realization, Wilczek’s vision triggered a new research field and became an inspiration to
Goes on to describe recent proposals and ends with:
that a current strong activity in the field of time crystals
will reveal novel phenomena that are difficult to discover
in condensed matter systems or simply overlooked so far.
Bearing in mind that a time degree of freedom adds an additional dimension, more possibilities for new discoveries are opened.
Nowhere in this review is a list for "practical applications'.
In general searches one finds vague proposals that time crystals will be useful for quantum computing:
While Yao is hard put to imagine a use for a time crystal, other proposed phases of non-equilibrium matter theoretically hold promise as nearly perfect memories and may be useful in quantum computers.
So, imo it is still at the research level, experimental and theoretical, and it is too soon to gauge the possible applications. After all when Maxwell came up with his equations which predicted electromagnetic waves, ~1860s Herz measured them in 1887, almost thirty years later, and the first practical application with communications happened in in the 1890's . At the time of the electromagnetic wave proposal wireless communications were not even dreamed about.
With our accelerated times ( 5 years between Wilczek's proposal and experiments, and the many researchers working away) applications should not be far away.