How to use the Ghost API to schedule an email-only newsletter

This ate an hour of my life, so maybe I can save you some time. For whatever reason, sending a post to the Ghost Admin API for emailing in the future is not a one-step process. Nope! You've got to first create it as a draft, then edit it. Here's the process:

async function pushPostToGhost(HTML) {
  const api = new GhostAdminAPI({
    url: process.env.GHOST_API_URL,
    version: "v5.0",
    key: process.env.GHOST_ADMIN_API_KEY
    });
// Change to when you actually want the email sent...  
    let schedule_time = moment().add(1, 'minutes').format('YYYY-MM-DDTHH:mm:ssZ');

    let post = {
      title: `Spiffy title`,
      html: `
      ${HTML}
      `,
      status: 'draft',
      tags: ['#some-tag'],
      email_only: true
      
    }
    let response = await api.posts.add(post, {source: 'html'});
    let edit = await api.posts.edit({
      id: response.id, 
      updated_at: response.updated_at, 
      email_only: true, 
      status: 'scheduled', 
      published_at: schedule_time
      }, {newsletter: 'default-newsletter', email_segment: 'all'
    });
      
    return edit; 
}

Huge kudos to the folks over on the Ghost Forum for discussion that got me there.