What is the 5/24 rule?
In the past year or so, Chase has frequently denied applications for certain cards (such as the Sapphire Preferred and Freedom) due to having opened 5 or more credit cards (with any bank) in the past 24 months. That means that anyone who regularly signs up for credit cards in order to earn points & miles is likely to be denied when they try to sign up for these cards. There are exceptions. It appears that being pre-approved for an offer may be the key to circumventing the rule (see this post, for example).
Which cards are affected by the 5/24 rule?
Currently, the 5/24 rule does not apply to co-branded cards (e.g. it does not apply to hotel or airline cards) and it does not apply to business cards. According to Doctor of Credit, though, the 5/24 rule will be applied to business cards beginning sometime in March 2016.
We don’t know at this time whether the 5/24 rule will be applied to co-branded business cards in March (such as the United Business card). My guess is that it will not.
Apply for Ink before March
If you have many new credit cards on your credit report and you’re interested in adding a new Ink card to the pile, I’d recommend signing up before March. Currently, the standard offer is for 60,000 points after $5,000 spend in 3 months. If you signup through a public offer online, the first year fee is not waived. If you signup in-branch, or receive a targeted offer, the first year $95 fee is waived.
To increase your chances of success, please read: How to get approved for the Chase Ink 60K offer.