ss="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 class="bp">self</span><span class="o">.</span><span class="n">_end_time</span> <span class="o">-=</span> <span class="n">delta</span>
        <span class="k">return</span> <span class="bp">self