n class="p">,</span> <span class="n">delta</span><span class="p">:</span> <span class="n">Optional</span><span class="p">[</span><span class="n">TimeDelta</span><span class="p">]</span> <span class="o">=</span> <span class="kc">None</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="s1">&#39;self&#39;</span><span class="p">:</span>
<span class="w">        </span><span class="sd">&quot;&quot;&quot;</span>
<span class="sd">        Shift the entire time range backward by a specified durat