You can set the temperature and the cook time on the device without having the app at all. The biggest benefit of the app is that you get a notice when the water is to temperature, which for certain more sensitive foods is needed to put the food in. (If you’re doing a 24 hour slow cook, it’s not really needed, but if you’re trying to do something with more precise cooking lengths, you don’t want the variance of starting water temp affecting how long the food is in the bath.)