Asklemmy

Hopper is an app that can show you when the best price is, and can recommend for you when to book your fight or give you alerts when the price drops. 3 weeks as others have recommended is generally an excellent sweet spot but it can also help give you a little more analysis. I highly recommend using it for that.

DO NOT under any circumstances actually book with them. They play elaborate games with the pricing (up to and including offering you coupons good for cash discounts on artificially-price-increased tickets so your discount works out to exactly $0), they add extra stuff to charge you for (including a $5 "tip") which the boxes for are checked by default. Booking with any third party as opposed to directly with the airline reduces some key benefits you'd otherwise get such as cancelling for free within 24 hours, which has screwed me before. Overall I'm sympathetic to their struggle to run a business which provides a service to people which gets them $0 revenue, and bravely trying to make it work anyway, but the way they do it is solidly customer-hostile.

Their features of watching the price and telling you when to book, last I checked, still work perfectly well and are excellent, though, and free if you never book with them.

I can’t source it, but a while ago i read that 3 weeks was the best time to get the lowest price.

I'd say somewhere before boarding.

7:32am

People keep saying 3 weeks which is odd to me. When I book a flight that close, I feel like I tend to end up paying more and/or having a very undesirable flight time or number of stops. Several months out is what I try to do for the cheapest flight at the most desirable time/number of stops.

International flights from NZ, 3 to 6 months. Local flights about 3 or 4 weeks.

I don't think it's going to be possible to give an absolute timeframe here as the answer is probably that it depends.

I lean toward booking early as that generally seems to be a better idea than the alternative.

Can't say timing-wise, but I did notice once that the prices were higher when browsing on my phone than on a desktop PC.

depends on many variables so there can never be a simple rule. Airlines want their planes full of paying customers is the real rule. They change prices based on how full each plane is. Sometimes a nearby city can be orth heading to for a much better deal.