填to
It's time to do sth 意思是是时间做某事了（到了做某事的时间了）.
It's time 后接动词用 to do 做目的状语
It's time 后接名词用 介词 “for”
eg：
It's time to have supper .是时间吃晚饭了.
It's time for supper .是时间吃晚饭了.
It's time for you to have supper .是你吃晚饭的时间了.