Reducing viewport framerate When I am in viewport → render mode, how can I reduce the re-render frequency of the viewport in Cycles engine mode?
So instead of it starting to render again when I slide any attribute in the material nodes, it would wait 250 milliseconds or more between each render on the right
Why? My computer is slow at rendering (weak CPU, no GPU) and I don't want to change all viewport/final render subdivisions, and number of samples each time I preview
I don't think that is an option, but here are some general tips.
In Rendered View, there's a button in the top right to pause rendering.

In Render Properties there's a Simplify section you can use to cut down several of the most taxing effects without having to make any changes to the objects in the scene.

If the problem is not the scene geometry, but rather the amount of time it takes to run individual samples, then I suggest a render region with Ctrl + B.  You could also use Local View with / to focus on your selection.