Pop wrote:

It's more energy-efficient to finish the shower, then turn on
the fan switch, and let a humidistat turn off the fan.

I disagree.

Why? Say 1.25 gpm of 105 F water comes out of the shower for 10 minutes,
and the bathroom air is 70 F at 50% RH to start with, and we a) run a
50 cfm fan during the shower and afterwards until the bathroom reaches
60% RH, or b) run it afterwards until the RH reaches 60%...

Nick