It took us 5h from the Palmer lodge (SH7) via Sylvia tops. The Sylvia tops are really easy walking but the last drop to the biv required some scrub bashing for the final 100m. Around 2h to Nina hut or 4h to Upper Nina if you shortcut at the 950m elevation directly to the Nina river (easy bushbashing on the spur).
Great spot, and a newish build but sadly the walls and roof inside the biv have mould, despite a vent above window. The door to the long drop has been blown off.