As I understand it, written once it'd be like 'At a time, Raj goes to Delhi' or something less awkward. The repetition turns it from 'a time' to 'sometimes'.
It happens quite often with adverbs, in Indian English too, though sometimes the only difference is linguistic flair, as far as I know.
Similarly to 'vite-vite!' in French, or someone I used to know (perhaps unique, perhaps dialectical) who said in English 'just and just', to emphasise how 'slightly' or 'only just' something was.