an hour later 还是Late

问题描述:

an hour later 还是Late
例如:my alarm didn't ring,so i woke up an hour _________ .
似乎用Late 和 Later 都见过,

按照句子的意思应该是填late, 闹铃没响,所以我起晚了一个小时.
Later放在时间之后,表示一小时之后