Based on historical data, good luck figuring out... some time its 3 months in advance, sometime its 6 months in advance... there's really no set time as to when you can book a flight. Best thing to do is to check the jetBlue website like almost every day. The pattern seems to be that you can book further and further in advance, at the same time, the further out you book, the greather chance of your flight schedule being changed based on my experience... but at least jetBlue try to accomadate you on a different flight if the schedule change doesn't meet your schedule.