When the peripheral device is in advertising mode it sends advertising packets at a fixed interval, as short as 20 milliseconds or as long as 10.28 seconds. A short interval allows the central device to find the peripheral quickly, but because it requires frequent radio work the power consumption is higher. It is therefore a balancing act between speed and battery use.
The advertising interval is completely under the peripheral device’s control. This is unlike the other connection parameters, as you’ll see below, which are suggestions that the central device can ignore.
The interval is set using setAdvertisingInterval: a function in the BLEDevice class of BLE_API. The function accepts a value in milliseconds.