 class="sd">        :rtype: self</span>
<span class="sd">        &quot;&quot;&quot;</span>
        <span class="n">delta</span> <span class="o">=</span> <span class="n">delta</span> <span class="k">if</span> <span class="n">delta</span> <span class="k">else</span> <span class="bp">self</span><span class="o">.</span><span class="n">delta</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">_start_time</span> <span class="o">+=</span> <span class="n">delta</span>
        <span cl