Run two clocks on every assessment. The calendar clock schedules a review at least yearly, shortened where the environment shifts quickly or the consequences of error are severe; a depot that reorganises weekly needs more frequent attention than a stable office. A calendar review can be brief when nothing has changed. Its value is the recorded confirmation that a competent pair of eyes asked the question, plus the first step of the method repeated: looking again for hazards that were not there before.
The event clock overrides the calendar whenever reality moves first. Accidents and near misses, new machinery or substances, altered processes, staffing changes and new regulation all knock out assumptions the assessment was built on, so the review happens immediately rather than at the next anniversary. Organisations that only ever review on schedule end up with documents describing operations that no longer exist, which is precisely the failure the validity test in the law is aimed at.