I agree with Ngaire, unless you have some special excursion planned for that day, like a 4x4 in the mountains, or plan on being in a rental car around Tahiti Nui/Iti and want to make the most of it, there's little reason not to board fairly early. You can always get back off the ship and explore downtown Papeete.
Egret, I'm with you! Bring on the PG air specials, and I'll be there!