Official period is 6 months for any bank or any card (for Online route). Through agents/Branch after 1M or sometimes 3M (if credit card account not updated properly). BOB allows 2nd card, why don't you try that through c2c and if you get higher limit close low limit card without worrying about all these.
Currently 2nd card possible through agents/branch, as Online some getting issues (because they're showing 2nd card as additional card in netbanking).