I've just read this and found it interesting. Their overnight mash dropped to 20°c with seemingly no ill effects.
http://brulosophy.com/2018/01/08/mash-length-overnight-vs-60-minutes-exbeeriment-results/
http://brulosophy.com/2018/01/08/mash-length-overnight-vs-60-minutes-exbeeriment-results/