It's time ( )(get) up.

it is time to do sth 是该做什么的时候了。
所以这里应该填写to get
如果是
it is time that...的句式的话，就要用虚拟语气，用动词的过去式。
it is time that we got up.

It's time ( to get) up.

to get
是起床的时间了

It's time do sth

所以是It's time ( to get) up.

to get ,或getting
It's time 后可加to do sth 或 doing sth,get是动词，to get和getting都行