well if the event dosent start till the 31st why would you get a box before then, is it stated that you can recieve it now?

It doesnt say anything about buying olives, only spending them. I'd wait until the event starts just to be on the safe side though.

The information is contradictory.. in one place it says that "the more olives purchased the more giftboxes available for redemption".

And in another place it says "Giftbox is ALSO paid by spending 100 olives from nf item store only".

So... does that mean you get boxes from both buying the olives and then spending them?

They meant spend. So i'm pretty sure if you have Olives right now, hold on to them till the event then spend it. 

I don't think purchasing olives factor into it, only spending.