Four roles, not four people
Someone who owns the measurement and keeps the conditions identical between rounds. Someone who can change the website - in practice the single most common bottleneck, because site changes usually sit with a team that has other priorities. Someone who can write with specifics, which requires access to the people who hold the facts. Someone who decides what gets published, especially the uncomfortable parts.
In a small company one person can hold three of these. The one that cannot be shared is the last: publishing limits and constraints is a commercial decision and needs someone who can make it.
The cadence
Measurement runs monthly at most and quarterly at least, always in the same one-to-two-day window, always with the frozen question set. Content ships continuously, but is not expected to show up in the next measurement - allow a round or two of lag. Placement happens in sets, timed so a set completes before a measurement round rather than during it.
What to review and when
Monthly: what shipped, what was placed, any access failures. Quarterly: the measured figures, against the same question set, with competitor figures alongside. Annually: whether the question set still reflects how buyers ask, and a new version if not.
Where it usually stalls
Site changes queued behind a product roadmap. Content that cannot get specifics because nobody will approve publishing a price. A measurement owner who changes jobs, taking the undocumented procedure with them. All three are avoidable by writing the procedure down and agreeing the publishing scope before the work starts, not when the first draft is blocked.