  The limiting temporal resolution of a time-domain survey in detecting
transient behavior is set by the time between observations of the same sky
area. We analyze the distribution of visit separations for a range of Vera C.
Rubin Observatory cadence simulations. Current simulations are strongly peaked
at the 22 minute visit pair separation and provide effectively no constraint on
temporal evolution within the night. This choice will necessarily prevent Rubin
from discovering a wide range of astrophysical phenomena in time to trigger
rapid followup. We present a science-agnostic metric to supplement detailed
simulations of fast-evolving transients and variables and suggest potential
approaches for improving the range of timescales explored.
