  Variability of active galactic nuclei (AGNs) has long been servicing as an
essential avenue of exploring the accretion physics of black hole (BH). There
are two commonly used methods for analyzing AGN variability. First, the AGN
variability, characterized by the structure function (SF) of a single band, can
be well described by a damped random walk (DRW) process on timescales longer
than ~weeks, shorter than which departures have been reported. Second, the
color variation (CV) between two bands behaves timescale-dependent, raising
challenges to the widely accepted reprocessing scenario. However, both the
departure from the DRW process and the timescale-dependent CV are hitherto
limited to AGNs, mainly quasars, at the supermassive scale. Here, utilizing the
high-cadence multi-wavelength monitoring on NGC 4395 harboring an
intermediate-mass BH, we unveil at the intermediate-mass scale for the first
time, prominent departures from the DRW process at timescales shorter than
~hours in all three nights and bands, and plausible timescale-dependent CVs in
the two longest nights of observation. Furthermore, comparing SFs of NGC 4395
to four AGNs at the supermassive scale, we suggest a new scaling relation
between the timescale (\uptau; across nearly three orders of magnitude) and the
BH mass (M_BH): \uptau \propto M^\gamma_BH where the exponent \gamma is likely
~ 0.6 - 0.8. This exponent differs from most previous measurements, but
confirms a few and is consistent with a recent theoretical prediction,
suggesting a similar accretion process in AGNs across different mass scales.
