  The concept of twistronics and moir\'e physics, which is present in twisted
two-dimensional bilayer materials, has recently attracted growing attention in
various fields of science and engineering such as condensed matter physics,
nanophotonics, polaritonics and excitonics. The twist angle between the two
layers has offered an additional degree of control over electron and photon
interaction with such structures. Inspired by the photonic version of
twistronics, here we introduce and investigate theoretically the temporal
analogue of twistronics in anisotropic optical media. We study how a
monochromatic electromagnetic plane wave propagating in a spatially unbounded,
anisotropic medium undergoes major changes when the relative permittivity
tensor of the medium is rapidly changed in time to create a new anisotropic
medium that is the rotated version of the original medium. We consider both the
elliptic and hyperbolic anisotropic scenarios. The propagation-angle-dependent
forward (FW) and backward (BW) waves with their converted frequencies and
relative amplitudes are obtained. To concentrate on the main features of this
concept without getting into details of dispersion, in our work here we assume
dispersionless and lossless material parameters. Our results reveal how
frequency conversion is highly dependent on the direction of propagation of the
original wave, rotation angle, and initial values of the material parameters,
proposing another class of "magic angles" for such temporal twistronics.
