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.The question asks for a general answer but gives only one special context.In general, only and but only are not substitutable.*they but only work that way occasionally.Which is grammatically correct?I can only do so much in this time.
Bailey's Synthetics | BONES
Bailey's Synthetics | BONES

Bailey's Synthetics | BONES of Only Bailey Tow Ball Exposed: The Real Reason For Those Sudden Breakdowns. .

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Or i can do only so much in this time.When only after, only if, only in this way etc.Are placed at the beginning of the sentence for rhetorical effect, the subject and auxiliary are inverted:Only after lunch can you play.