I would like to know that, too (and how the whole concert stuff works e.g. is it better to be at the concert location hours before it starts?)
I can't answer the first question considering I practically look Japanese. As for being on time, that really depends on what your purposes are besides attending the concert. For example, if you're thinking of purchasing tour goods, it'd be better to be at the concert grounds several hours before it starts since the line wouldn't be
extremely long at that time. Of course there's also the option of shopping afterwards, but certain things tend to run out of stock.
If you're just in it for the concert it doesn't really matter, but it's good to keep in mind that they open the doors like an hour in advance. If you're new to this, finding your seat can take a while.
Also, unless it's necessary don't bring any cameras with you since the staff will temporarily confiscate it if they find it.