Why every four weeks instead of monthly?

Because the work runs in four-week cycles, and billing on the same cycle keeps the work and the invoice lined up. A calendar month drifts against the actual work.

• The report, the Google posts, and the new pages all run on a four-week rhythm.
• Billing on that same rhythm means every invoice matches a completed cycle of work.
• Practically, that is thirteen billing cycles a year instead of twelve, and Own The Box Marketing says so plainly rather than burying it.

It is the honest way to bill for work that happens in cycles. You are paying for a completed round of work each time, not a square on the calendar.