It might be nice to putthe ferroresonant downstrem of the timer, from a sound perspective, but the light output could be non-linear to time for shorter expsoures.

Ferroresonant units stabilise output by building and storing a surplus of energy in the form of an extra winding that will keep the magnetic core that powers the output winding at a constant output level over short perionds of time. It does take time to build up that field, and while doing so, the enrgy is not available to go out as ouput power.

Kind of like adding extra mass tuned to adjust the resonant freqency of the suspension of a motor vehicle. Makes for a smoother ride, but the extra mass means moderatly slower acceleration from a stop.

Also when you stop the power, the ferroresonant dumps the extra energy stored in it, but not necessarily in the same voltage profile that it absorbed it in at at the start of the process.
So the light may have a differnet intensity/colur at the end as extra field collapses.