  We have recently shown that a `sphere+disk' geometry Compton corona model
provides a good description of Rossi X-ray Timing Explorer (RXTE) observations
of the hard/low state of Cygnus X--1. Separately, we have analyzed the temporal
data provided by RXTE. In this paper we consider the implications of this
timing analysis for our best-fit `sphere+disk' Comptonization models. We focus
our attention on the observed Fourier frequency-dependent time delays between
hard and soft photons. We consider whether the observed time delays are:
created in the disk but are merely reprocessed by the corona; created by
differences between the hard and soft photon diffusion times in coronae with
extremely large radii; or are due to `propagation' of disturbances through the
corona. We find that the time delays are most likely created directly within
the corona; however, it is currently uncertain which specific model is the most
likely explanation. Models that posit a large coronal radius [or equivalently,
a large Advection Dominated Accretion Flow (ADAF) region] do not fully address
all the details of the observed spectrum. The Compton corona models that do
address the full spectrum do not contain dynamical information. We show,
however, that simple phenomenological propagation models for the observed time
delays for these latter models imply extremely slow characteristic propagation
speeds within the coronal region.
