I can't wait to drink it. I don't think you need the heater, if you have the mash in a cooler. I did a partial mash soured a while back, about 30% by weight, and kept the lid on it for (I think) 24 hours. I basically followed the BYO web article on sour mashes. httpss://byo.com/stories/item/1691-sour-mashing-techniques
I picked up the process idea from https://anarchylane.com/blog/?p=1442
I don't anticipate going past 24 hours, but I want to be prepared. We shall see.