Dielectric adaptor for galvanized to brass pipe?

I know you are suppsed to use an adaptor between copper pipe and galvanized steel pipe.
I recently used brass with galvanized pipe in a short span. How long does it take for electrolytic corrosion to become a problem? or is it no problem?

Answers:
You don't mention the application but a simple water line 10-15 years.

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