JetBlue just extended their schedule to allow you to book flights through February 13, 2018. While most larger airlines allow you to book travel 330 days in advance, JetBlue extends their reservations systems a few months at a time. Up until now you could only book through the beginning of August, so this means you can now for MLK weekend. Flights for Presidents Day weekend are still not available though, but should be at some point in July. Keep in mind that flights during peak times will most likely be cheapest today.
I know booking this far ahead of time is nerve racking as you do not want to book a flight and then have to change or cancel it – and those fees are not cheap! However, if you have JetBlue Mosaic status, you can always cancel and rebook your flight for no fee. Also for all other passengers, if your flight goes down in the next 5 days, you can get a credit for the price difference.