The US Cybersecurity and Infrastructure Security Agency (CISA) has recently reviewed the guidelines (actually a Binding Operational Directive for US Federal Agencies) on patching (see the Directive here and a comment here).
Now vulnerabilities rated “critical” (according to CVSS version 2) must be remediated within 15 days (previously it was 30 days) and “high” vulnerabilities within 30 days from the date of initial detection by CISA weekly scanning.
Due to the short time between detection and remediation of vulnerabilities, applying patches in time is going to be difficult, due to the possibily missing availability of patches by the vendors and the time needed anyway to test them in each IT environment.
This implies that there must be in place processes to design, test and deploy temporary countermeasures to minimize to an acceptable level the risks due to these vulnerabilities. And these processes must be fast, they should take at most a few days.