The BM/RM can upgrade the account instantly if they want to and hold that stature as long as they want.
About the 3 month thing, HDFC itself will automatically upgrade your account without your BM/RM intervention. So. in your case, your BM has just laid out the general rule of HDFC and not giving you any form of preference.
Generally, if the BM/RM thinks that you can be a potential asset for the branch in the long run then they can give out things like account upgrade or cc.