Manipulating variables between BLE advertising?

You can't have code in Espruino that is called each time an advertising packet is sent, but probably the best method is just to use setTimeout?

var idleTimer;

function updateBluetooth() {
  // setAdvertising...
}

function newDataPulse() {
  power = ...;
  updateBluetooth();
  if (idleTimer) clearTimeout(idleTimer);
  idleTimer = setTimeout(idleHandler, 60000);
}

function idleHandler() {
  idleTimer = undefined;
  power = 0;
  updateBluetooth();
}