It takes around 10 seconds on my machine, but it is so because i pinned the nixpkgs entry in the flake registry to the one currently in use.
$ time nix search nixpkgs neofetch
* legacyPackages.x86_64-linux.freshfetch (0.2.0)
A fresh take on neofetch
* legacyPackages.x86_64-linux.neofetch (2020-11-26)
A fast, highly customizable system info script
real 0m10,138s
user 0m7,766s
sys 0m1,011s
By default it points to the bare nixpkgs repo (master branch) and so nix downloads a new version of it most of the times.