Serious time to set up _and_ maintain as the project changes. At least, that was my experience. I really _want_ to have Nix-powered development environments, but I do _not_ want to spend the rest of my career maintaining them because developers refuse to "seriously dig" to understand how it works and why it decided to randomly break when they added a new dependency.

I think this approach works best in small teams where everyone agrees to drink the Nix juice. Otherwise, it's caused nothing but strife in my company.