slack.crime.js

async function setLotsOfReminders(name, reminder, times) {
  await Promise.all(Array.from({ length: times }, (_, i) => i + 1).reduce(async (p, days) => {
    await p;
    document.querySelector('[role="textbox"]').innerHTML = `remind @${name} to ${reminder} in ${days} days at 4am`;
    return new Promise(resolve => {
      setTimeout(() => {
        document.querySelector('button[aria-label="Send message"]').click();
        setTimeout(resolve, 1000);
      },  1000);
    });
  }, Promise.resolve()));
}

setLotsOfReminders('sentreh', 'do the thing', 1000);