Several years ago I turned up a couple of hours ahead of time at Christchurch NZ airport because I needed to be out of the hotel. This wasn't a standby fare though, it was economy booked a couple of months previously.
It suited Air New Zealand to put me on to an early flight and not only that, upgraded me to business class.
You may be lucky, you may be not. But you definitely won't be lucky if you're not there early.