code: public boolean isTileToBeDownloaded(final ITileSource pTileSource, final long pMapTileIndex) {
          final Long expiration = mTileWriter.getExpirationTimestamp(pTileSource, pMapTileIndex);
          if (expiration == null) {
              return true;
          }
          final long now = System.currentTimeMillis();
          return now > expiration;
      }
docs: "Should we download this tile?", either because it's not cached yet or because it's expired
  
  @since 5.6.5