It's pretty fast, especially if you don't get into flakes right away. You basically just install nix with a one liner -> install home-manager through nix -> start adding packages to list.

Here's a comment I made when I was starting out with basic instructions. Do note I'm now using this command for updates instead (updates hm, package definitions, and the packages themselves)

cd ~/dotfiles/nix/ && nix flake update && nix-channel --update && home-manager switch --flake ~/dotfiles/nix/