I am not sure I understand the question, but perhaps [this](https://english.stackexchange.com/a/5763/4040) will answer it:


> Definitions for *it* in my *Webster's 3rd New International
> Dictionary* include:
> 
> > **2a** used as an expletive subject of an
> > impersonal verb that expresses a
> > simple condition or an action without
> > implied reference to an agent about
> > the weather ... or time.
> 
> *It is raining* or *It is two o'clock* are examples of 2a.