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It's different for everyone. I've requested 6 CLI's with Citi, 5 were SP's & 1 was a HP.
I was lucky enough to get SP both times I asked for a CLI. I do use the card heavily though and PIF every month.
They HP the hell out of me when I requested CLI at 6 months. Honestly, with them I'd wait like year before I ask for anything. Or just let them do it when they feel to do so. PCing though with them is easy I found out.