It was five o'clock yesterday afternoon when I was going home by bus.
昨天下午,当我准备回家的时候,时间是5点.
when I was going home by bus是时间状语从句,不是强调句型.
强调句型是It is / was...that / who...,确定句子的主语、宾语、状语.
下面的句子才是强调句型：
It was at five o'clock yesterday afternoon that I went home by bus.