We have one coming up this weekend: the "Spring forward" one hour shift to daylight savings time.
A good time, in between complaints about losing an hour's sleep -- to remind yourself to
Check all anti-virus, anti-malware defenses to ensure that they're up-to-date
Review all patch settings and deployments (Firefox issued a major update this past week, and Microsoft has at least one critical patch coming next Tuesday.) Take a look at who has access to what on your network, reducing authorizations where possible.
Perhaps most importantly, calendar-linked security procedures give you a convenient opportunity to remind all computer-users on your staff or in your company to:
Change their passwords, reminding them as well of strong password techniques, and the importance of never sharing passwords (or even writing them down.)
Calendar-based security reminders are also a convenient opportunity to review your security policies, revising and extending them as needed.
Whether you choose daylight savings shifts as one of your calendar checkpoints, it's worth considering using calendar events as security spurs. They're on virtually every calendar and, in the case of holidays (do the security checks and updates the day before a holiday) they're on everybody's mind.
And if you use the Spring timeshift as a security reminder, you'll still lose that hour's sleep, but the sleep you get will be easier.