句子：I am thinking back now to when I first started listening to rock&roll and I remember my father saying it was a bad influence on us.

请问老师：back now to是短语介词back to中插入了now，还是副词back修饰thinking，now时间状语，to when...作状语呢？back to、up to与down to类似的短语，其中back， up， down的词性能不能分析呢？他们是修饰to...还是修饰前面的动词或非谓语动词呢？