楼主说的关系代词是定语从句里的那个吧?（which that who whose whom.）
定语从句的时态（即关系代词后的时态）由从句本身的意思决定.比如：
—He is monitor of our class,who [is] easy to get along well with.
这里从句阐述的是一个事实,故用一般现在时
—I went to the factory again which we [visited] last week.
去工厂这个动作发生在过去,所以用一般过去时
—The task that we [have been doing] since last night is so difficult.
这里强调“从昨天晚上开始我们一直都在做的这个任务”,所以从句用了现在完成进行时
甚至还可以在定语从句中插入条件状语从句.这里从句用了过去将来完成时：
—I greatly appreciate his generosity,without which we [wouldn't have completed] our work in time.
综上所述,定语从句的时态没有什么限制,完全由从句表达的意思来决定.
望楼主能理解.