Best time to book flight from the east coast?

I don't sail on the POA until April 2018. I'm not sure how far in advance I should book the airfare.

Any thoughts?

There is no magic time to book your flights. If there were, the airlines would figure out everyone was waiting for that magic time, and raise the prices then.

April is a shoulder season in Hawaii, so air fares might be a bit lower. United just announced additional non-stop flights from ORD and EWR non-stop to HNL. So, what I would do is start monitoring the fares. I would bet in a couple of months, the fares will drop some. I would then buy, and not look back. Or, if you see them dropping in the next few weeks, after the rush is off from the new announced flights, book.

Where on the East Coast? My wife and I booked a round trip flight to HNL from Montreal for less than $1000 US for the two of us. That is almost $800 less than from New York or Boston. Since we live in Vermont it is actually closer than either Boston or New York as well. We will be flying a week after Thanksgiving. So be sure to check all you local options, even Southwest Airlines to get you to the West Coast where you can connect to the more frequent flights to Honolulu available from several carriers from Los Angeles, San Francisco, or Seattle.

I fly from LAX but would think that from the East Coast the slow times with the best airfares would be at the same time. The period of time between Thanksgiving & Christmas have the cheapest airfares to Hawaii and the next lowest prices are from about mid-April to the first week of June. This is a slow time for visitors between Easter & summer vacation with big price increases for summertime.

These are the trends however when the lowest airfare is available will vary depending upon passenger load levels & only the airline's system algorithm knows for sure.

If I was flying in mid-April then I'd think that after the holidays prices may drop. But I'd regularly track prices & when finding an acceptable price would book it & as Bruce said never look back.

I don't know how NCL's airfare program works but with Princess their EZair Flexible airfares can be booked with the option to refare at a lower price. Airfare is paid with the cruise's final payment which is generally 75 days before sailing. If NCL has a similar program where it's possible to get a lower price that could be another option to consider.