When your facial hair constitutes, unequivocally, a beard. Or when your facial hair is now a sign of a deliberate aesthetic choice. This is opposed to someone who simply hasn't shaved in a while or keeps a token amount of short facial hair that really just makes them look lazy or because they are lazy.
"My whole face looks longer today, it must be because I passed the beard threshold"
x- "What do you think of my new beard?"
y- "that's not a beard, you haven't reached the beard threshold"
x-"but I haven't shaved in like 5 days!"
y-"It's still a little patchy, you'll hit the beard threshold soon."scruff
, peach fuzz
, facial hair