Is anyone actually doing this successfully for a 5 gallon mash? What wattage cooker are you using? Are you able to step to other temperatures fairly quickly?
Here's an article about someone using an Anova cooker with a BIAB method for 5 gallons. https://anovaculinary.com/brewing-beer-with-the-anova-one/
It mentions getting fro 152 to 170 in 15 minutes with just the sous vide cooker and no help from a burner.
You can also check out Brian at Short Circuited Brewers YouTube video of this in practice. I believe the one he has in the video was an Avalon Bay and Inkbird also has a 1000w model out I came across on Amazon.