It's instant, based on perception of decline.
Spencer ’2 [Jack; 2000; Research Fellow in Nuclear Energy Policy at The Heritage Foundation's Roe Institute for Economic Policy Studies; Heritage, “The Facts About Military Readiness,” http://www.heritage.org/Research/Reports/2000/09/BG1394-The-Facts-About-Military-Readiness]
Military readiness is vital because declines in America's military readiness signal to the rest of the world that the United States is not prepared to defend its interests. Therefore, potentially hostile nations will be more likely to lash out against American allies and interests, inevitably leading to U.S. involvement in combat. A high state of military readiness is more likely to deter potentially hostile nations from acting aggressively in regions of vital national interest, thereby preserving peace.