We should create a TimeStamp class to avoid confusion of what time is used. Currently we have lots of places that expect something like a "long timestamp" without specifying whether this is currentTimeMillis, elapseRealTime, uptimeMillis, or something else.

Something like this might work:

class TimeStamp {
  public TimeStamp() {
    // Uses appropriate method to determine "now".
  }

  public long getElapsedMillis() {
    // Uses matching method to determine duration.
  }
}