It really depends on the blind structure of the tournament. If it's a turbo, you're probably going to be registering with 1-2 bb's if you register that late. Some people like to register late for a rebuy, and register, take the rebuy, and then the add-on. If you're playing a deepstack tournament with long blind levels, you don't put yourself at a big disadvantage by registering late.

Personally I always try to register within the first blind level, lots of monkeys throwing chips around then.

But as is the case with most poker questions, the answer is "it depends".