"Aamir comes at nine now."
Translation:अब आमिर नौ बजे आता है।
I take the difference between: "आमिर अब नौ बजे आता है।" and "अब आमिर नौ बजे आता है।"
As analogous to the difference between: "we are now (currently) talking" and "now we're talking".
I.e. putting it at the very beginning indicates a change in state as opposed to a reference to what is currently happening.
But I'm a learner just like you guys. I'd love to hear a native speaker weigh in.