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Typically in the first 60-90 days if yuo're going to see an auto increase that's when.
The system will auto reject a manual increase during the first 90 days typically.
Every other month seems to be ideal for hitting the button and getting the most per request for me at least. Others hit the button every 30/90 days with mixed results.
The manual requests usually result anywhere from $500-$8K depending on your profile.
http://ficoforums.myfico.com/t5/Credit-Cards/Discover-unOfficial-Data-Points/m-p/4802538