  We present 17 nights of ground-based, near-infrared photometry of the
variable L/T transition brown dwarf SIMP J013656.5+093347 and an additional 3
nights of ground-based photometry of the radio-active late M-dwarf TVLM
513-46546. Our TVLM 513-46546 photometry includes 2 nights of simultaneous,
multiwavelength, ground-based photometry, in which we detect obvious J-band
variability, but do not detect I-band variability of similar amplitude,
confirming that the variability of TVLM 513-46546 most likely arises from
clouds or aurorae, rather than starspots. Our photometry of SIMP
J013656.5+093347 includes 15 nights of J-band photometry that allow us to
observe how the variable light curve of this L/T transition brown dwarf evolves
from rotation period to rotation period, night-to-night and week-to-week. We
estimate the rotation period of SIMP J013656.5+093347 as 2.406 +/- 0.008 hours,
and do not find evidence for obvious differential rotation. The peak-to-peak
amplitude displayed by SIMP J013656.5+093347 in our light curves evolves from
greater than 6% to less than 1% in a matter of days, and the typical timescale
for significant evolution of the SIMP J013656.5+093347 light curve appears to
be approximately <1 to 10 rotation periods. This suggests that those performing
spectrophotometric observations of brown dwarfs should be cautious in their
interpretations comparing the spectra between a variable brown dwarf's maximum
flux and minimum flux from observations lasting only approximately a rotation
period, as these comparisons may depict the spectral characteristics of a
single, ephemeral snapshot, rather than the full range of characteristics.
