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.Which is grammatically correct?I can only do so much in this time.Or i can do only so much in this time.The question asks for a general answer but gives only one special context.In general, only and but only are not substitutable.
Most Rage Inducing Games Of All Time
Most Rage Inducing Games Of All Time

Most Rage Inducing Games Of All Time of The Only Vibrant Summer Nail Colors Guide You'll Ever Need This Summer. .

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*they but only work that way occasionally.