Have read about people just using ice cubes, but have also read that it doesn’t actually do much/anything if it’s not done for a prolonged time. It’s better to keep the whole grow room cool for flower period as a way to manage temperature for better output (in color/potency).
A period of darkness before harvesting is what I’d recommend (and will continue doing). Around the 36-72 hour mark there is a noticeable change in smell, and from other research I’ve done on the subject it does seem to be beneficial in other measurable ways.
This was just one experiment related to that but is interesting to see. It would be nice if there was more data out there on this: