It's time to跟的是不定式（to do）.也就是说,要跟一个动词,意思是“到做某事的时候了”.如：It's time to go home.It's time to tell him the truth.
It's time for 跟的是名词.也就是说,不能跟动词.如：It's time for lunch.(没必要说It's time to have lunch)It's time for class.(没必要说It's time to begin the class.)
所以选B