  The temporal behaviour of X-rays from some AGN and microquasars is thought to
arise from the rapid collapse of the hot, inner parts of their accretion discs.
The collapse can occur over the radial infall timescale of the inner accretion
disc. However, estimates of this timescale are hindered by a lack of knowledge
of the operative viscosity in the collisionless plasma comprising the inner
disc. We use published simulation results for cosmic ray diffusion through
turbulent magnetic fields to arrive at a viscosity prescription appropriate to
hot accretion discs. We construct simplified disc models using this viscosity
prescription and estimate disc collapse timescales for 3C 120, 3C 111, and GRS
1915+105. The Shakura-Sunyaev {\alpha} parameter resulting from our model
ranges from 0.02 to 0.08. Our inner disc collapse timescale estimates agree
well with those of the observed X-ray dips. We find that the collapse timescale
is most sensitive to the outer radius of the hot accretion disc.
