I think the 90 days is important with Citi more so than most other credit card companies. When it comes to Chase it's more about what your relationship is with that bank. Balance, credit line, payment history, etc. If you establish a good relationship I don't think it matters when you apply for cards. However... it probably makes more sense to spread them out quarterly because it is easier to explain the credit "hits" every few months vs. monthly. Of course this is just my opinion...