This feature is not on a current W3C standards track, but it is supported on the Firefox OS platform. Although implementations may change in the future and it is not supported widely across browsers, it is suitable for use in code dedicated to Firefox OS apps.
discoverableTimeout property indicates how long (in seconds) the device remains discoverable.
var timeout = instanceOfBluetoothAdapter.discoverableTimeout
Return a number.
Not part of any specification yet. It should be discussed as part of the W3C's System Applications Working Group.