Join Date: Oct 2014
Location: USA
Programs: Chase Ultimate, Amex, Delta, AA, BA Avios, United, US Airways, Marriott, Hilton
Posts: 260
18 mo clock refers to having the card opened or closed.
A denial does not qualify as an opened card nor a closed card, so this will have no impact on any 18 mo time frame you are keeping track of.
Good luck.