CVs done only when job-searching produce vague, generic documents. By the time you need one, specifics from 6-12 months ago have faded. Quarterly updates preserve specifics that compound into compelling CV.
What to add quarterly
Specific accomplishments with metrics. Projects completed and outcomes. Skills developed. Trainings or certifications. Positive feedback received verbatim. Each entry takes 15 minutes; cumulative effect over years is substantial.
When the time comes to use the CV (opportunity, redundancy, internal application), the document is ready. The 30 minutes quarterly is the maintenance; the readiness is the payoff.