The short answer is that bluetooth headphones are safe to use any time wired headphones are allowed*. Bluetooth already has interference reduction built-in to the design, and on top of that most devices now use the bluetooth low energy spec. Unless that is, they are cheap and/or unlicensed devices (often referred to as 'Blue Tooth' or Blue-Tooth to avoid trademark infringement).
Additionally modern aircraft are also more resistant to interference, especially from consumer devices. *Some devices, especially older medical implants like pacemakers, are still sensitive to BLE at close range; and generally speaking the people who are affected are already aware.