I consider it an early pull if I popped it and didn't have time to reach it before it died.
One Croque I was the only one at the node. I waited till near the end to hit it, presumably it popped because I heard a billion shouts and it was dead before I even got there. There are other examples - sometimes I'll pop something like Brontes or Croak. 30 seconds later someone pulls.
I've also had S ranks where the wait was nearly 10-15 mins and people still were crying early pull /rolls eyes
In general I consider it only polite for at least the travel time to the hunt + 1 minute after you get there. Ideally 5 mins on an S rank was considered polite but you'll always have someone showing up late and whining that it was an early pull (In which case said person needs a better LS) But if you're pulling the moment you get there, it's probably too early. Waiting at least 1 minute after you get there is considered polite.
But yes there's no such thing, technically, as an early pull. SE originally pitched it as as 'you're running through the zone and find a hunt, you beg/cajole your FC mates into showing up to kill it'. People found that it was possible for lots of people (not just 1 person/party/alliance) to get full credit so a LS relay community was born. Being impatient and pulling 'early' just goes against that community spirit.