I want to share a strategy I've worked out for determining cooking times. This is all about short-cooking (without added time for tenderization).
When I first got the Sous-Vide Dash app, I was confused that the suggested times were all much longer than times given in the tables in Modernist Cuisine. In some cases the differences were close to 50%. I exchanged some emails with Darren Vengroff, the app's developer, who explained that the app strictly follows the best models for heat propagation. The issue is the long tail of the curves: you might get within 1/2 degree after 30 minutes, but that last final bit can take a long time.
This is why Myhrvold recommends setting the circulator to 1°C higher than the target temperature. But I find that this still leads to surprisingly long cooking times.
It occurred to me that we habitually use the core temperature as the target temperature. This makes sense in cases where you need to pasteurize food all the way to the core, but in practice it means either 1) if you set the water bath temperature higher than the target, you will have a gradient, and every part of food besides the center will be cooked higher than the core, or 2) if you set the water bath exactly to the core temperature, cooking times will be extremely long.
After a bit of experimenting, I've started following the Mhyrvold recommendation of setting the bath 1°C higher than the target temperature, but then in the SV dash app, setting the core temperature 1/2°C LOWER than the target temperature. This achieves two things. It significantly shortens cooking times, actually bringing them into a range that's roughly similar to the MC tables. And the gradient, if it's perceptible at all, puts a larger portion of the food close to the target temperature.
Of course I'm not talking about huge gradients like you see in conventional cooking. I don't notice this kind of gradient at all when cooking beef. But with salmon, it's perceptible, and can actually be pleasant. You get a very subtle range of textures, from less cooked than the target at the center to slightly more cooked at the edge.