promise = promise.then(function() {
  // get epoch millis, convert to epoch micros
  var startMicros = 1000*timeWindow.start.valueOf();
  console.log("start: "+timeWindow.start.toISOString()+" "+timeWindow.start.valueOf());
  return dlConn.awaitDLCommand("POSITION AFTER "+startMicros);
}).then(function() {