Constant MIN_AUTO_ANNOUNCE_INTERVAL_S 

pub const MIN_AUTO_ANNOUNCE_INTERVAL_S: u32 = _; // 1_200u32

Shortest accepted PROP_ADVERT_INTERVAL / PROP_BEACON_INTERVAL, in seconds.

An absolute floor, and one a device may only ever round up from: scheduling jitter delays an announcement and never brings it forward, so no configuration can put an unsolicited broadcast on the air more often than this. The duty ledger remains the airtime control; this is what keeps a mistyped interval from spending the whole budget on announcements before anything else can speak.