Save-the-dates for a destination wedding go out fourteen months ahead of the wedding date. That is earlier than a local wedding (where six to eight months is the norm) because destination guests need runway to plan travel, block time off work, and budget for the trip. A destination save-the-date that arrives too close to the wedding produces two problems: guests miss the early airfare window, and some with firm work schedules cannot clear the dates at all.
Earlier than 14 months is fine. We have sent save-the-dates 16 and even 18 months ahead for weddings with signature venues booked two years out. The risk of sending too early is low; the risk of sending too late is real.