Guix seems to be building everything from source, which can take a while. As per these instructions I tried
# cd [prefix]/share/guix/hydra.gnu.org.pub # guix archive --authorize < hydra.gnu.org.pub and got guile: warning: failed to install locale warning: failed to install locale: Invalid argument with no other output. I get that error almost every time I try to do something with Guix and it usually works anyway. Since I got no other errors I just kept going with $ guix build emacs --dry-run and got "The following derivations would be built:" so apparently it did not work. During an installation I do see a lot of "updating list of substitutes" messages, but I also frequently see the word "build" and a lot of .c and .h files go by, which combined with the long installation time makes me doubt that it is actually downloading binaries from the substitutes and installing them.