You'll be able to assign your seats at no cost when check in opens 48 hours before departure but so will everyone else! This time last year the long hauls (In my and my colleagues' experience) were running 50-75% full, so it wasn't a big issue logging on 1 hour after check in opened and still being able to find a window or aisle (depending on your pref) seat. Now things have changed, Fiji has reopened and most long hauls this year are close to 100% full. When I logged on around 10 minutes after the 48 hour mark for my long haul in February, all that was left were middle seats towards the back. Not a mistake that has been repeated!