As to anything there are more correct answers to this question and it comes down to different variables:
-What kind of tournament are you playing?
-How high is the buy-in?
-How experienced are you?
-How many players are expected to register for this tournament?
-What is your style of play before you hit the final tables?
-And many more...
Objectively looking at it, early register should be favourable approach as you can play maximum amount of hands that way and probability to play better cards is greater that way. At the same time it's also a safer way to build a decent stack of chips, but due to subjective nature of a human being that might not always be true.
As many already stated, most of the "fish" players that play erratic are knocked out within first hour of the tournament and knowing how to mingle with them could net you a very juicy stack, but you don't always know who they are and they can push you out of hands that you should be winning against "normal" opponents and even when you dominate hands, poker can still be poker and screw you with insane flop to river cards.
Personally I take the following approach:
-Knock out/bounty builder tournaments I register as soon as possible, as you can collect quite some funds within first hour of play, feasting on that delicious fish.
-Higher buy-in tournaments I register within 45 min after start of it as you don't meet so many erratic players there.
-Lower buy-in tournaments I register with around 20 bb, try to avoid as many donkies and just go for the gamble with the few good hands I get.
This approach usually works the best for me, but at the end of the day a lot comes up to every single person and what works best for them.