time 做先行词的话定语从句中 能省略连接词吗?

在沪江关注英语的沪友vividilu遇到了一个关于留学考试的疑惑,已有2人提出了自己的看法

知识点疑惑描述:

托福TPO 阅读 Autobiographical Memory 中的一篇文章:其中的一个句子大家帮忙看一下吧: When researchers had one year olds imitates an action sequence one year after they first saw it, there was correlarion between the children's verbal skills at the time they first saw the event and their success on the later memory task. 其中:at the time they first saw the event 这里不明白为什么省略了连接词?

最佳知识点讲解
知识点相关讲解
at the time 本身就可以用作连词,等同when 。有很多短语做连词的 on the condition that, by the time that,now that,
—— lotusLI88
我觉得at the time 就是一个时间词组哈,为什么要用定语从句呢?
—— 姜志焕