In only when , there is a sense of urgency, a slightly more 'involved' writing. It was only when is by comparision more 'relaxed' writing, more like someone is recounting something to someone. I am from bangalore and people here tend use the word only to emphasise something in a sentence.

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What is the proper way to put it? I can only do so much in this time. Or i can do only so much in this time.