I've heard some members get converted as soon as 9 months. Regards the lenght of account, it should not be change at all unless the account number is change when converted, which I doubt it would.
I am sure you can get 2x CapitalOne, initial CL should be $300, 3 months on-time payment, it will be automatic increase to $500, wait 3 more months, call and request to have account close due to low CL, they will bump it up to $1000 (at least that how it works for me). Combine the 2 cards you have into 1, you will have $2000 CL, and by the end of this year CapitalOne will report CL.
I used to have the 99/500 from BoA. After 1 year of perfect payment and PIF, unable to convert to regular card with no explanation whatsoever. I closed out the account. 3 months later i still have not gotten my $99 deposit back. I have to call 2 times to have the $99 refunded to me. Overall, very unhappy with the service.
I am sure many other had better experience with BoA. But I will never go back with them.