  We report the observation of long-lived Floquet prethermal discrete time
crystalline (PDTC) order in a three-dimensional position-disordered lattice of
interacting dipolar-coupled 13C nuclei in diamond at room temperature. We
demonstrate a novel strategy of "two-frequency" driving, involving an
interleaved application of slow and fast drives that simultaneously
prethermalize the spins with an emergent quasi-conserved magnetization along
the x-axis, while enabling continuous and highly resolved observation of their
dynamic evolution when periodically kicked away from x. The PDTC order
manifests itself in a robust period doubling response of this drive-induced
quasi-conserved spin magnetization interchanging between x and -x; our
experiments allow a unique means to study the formation and melting of PDTC
order. We obtain movies of the time-crystalline response with a clarity and
throughput orders of magnitude greater than previous experiments. Parametric
control over the drive frequencies allows us to reach PDTC lifetimes up to 396
Floquet cycles which we measure in a single-shot experiment. Such rapid
measurement enables detailed characterization of the entire PDTC phase diagram,
rigidity and lifetime, informing on the role of prethermalization towards
stabilizing the DTC response. The two-frequency drive approach represents the
simplest generalization of DTCs to multi-frequency drives; it expands the
toolkit for realizing and investigating long-lived non-equilibrium phases of
matter stabilized by emergent quasi-conservation laws.
