Processing time for the I-130 itself is as estimated on the USCIS website.
However, your brother will then need to wait for his priority date to become current. Based on current priority dates, that is likely to take over 10 years.
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I agree with my colleague. Although the I-130 may be approved quickly, he will still have to wait for the priority date to become current.
You should still file as soon as possible, just to make the processing time even one day shorter.