it is time for bed .
是时候睡觉了.
it is time to后面加的是动词原形do,比如：it is time to go home
而it is time for后面接名词（或动名词）,比如it is time for lunch
把“it is time to ”句子的最后一个单词前面的动词去掉,
把it is time to变成it is time for,
句子的最后一个单词不变