Deployments are somewhat limited in that they do not define an exact time that updates should or must be installed; they merely define a time when updates become mandatory. This could easily cause disruption to your users and your servers if updates install at various times after the deadline.
Maintenance windows solve this dilemma. In general, maintenance windows prevent the ConfigMgr client from undertaking any action that could disrupt the end user or hosted services on a system. This includes preventing software updates deployments, software distribution advertisements, and restarts initiated by ConfigMgr for software updates.
Edit these schedules by right-clicking any collection and choosing Properties. This displays ...