Let's say its Sept 15th and we want to acclimate new corals for 5 days. The Coral Acclimation dialog is enabled, some reduction is set, and then the START DATE is set to Sept 15th and the END DATE set to Sept 20th (5 days of acclimation).
So the controller reduces the intensities starting today (Sept 15th) then gradually brings the intensities up until the clock reaches Sept 20th. On midnight Sept 21st, coral acclimation is turned off automatically.
Now, if the user sets the start or end date to times that have already passed, then coral acclimation will not turn on. Setting START to August 1st and END to Sept 1st (and right now it's Sept 15th), Coral Acclimation won't turn on. If the user goes back to dialog, it will show disabled no matter how many attempts are made to turn it on.