We do this all the time for our multi-step service setups. Just create the job with multiple visits scheduled out, but set your invoicing method to manual.
After the first main visit is completed, generate and send the full invoice for the entire job right then. The second visit will stay active on your schedule for the six-week checkup or takedown without generating a double invoice or messing up your billing.
Another clean way to handle it is putting both line items on the job, putting the full price on the first visit line item, and marking the second visit line item as $0. That way the customer sees both services clearly on the work order, but the full bill drops on visit one.