How can I schedule a post to publish every 45 days?

If your goal is to publish the same social post every 45 days, what you need to do, after publishing or scheduling it for the first time, is, you may go to Queue tab or Sent tab, find that post, click on actions on the right column, click the dropdown arrow and select 'Open as Copy', and then schedule that post for the next 45 days. You need to repeat the process until you reach the number of times you want that post published.