Once you have succesfully placed the first order, subsequent orders are automatically placed when < 1/3 of certificate validity remails (e.g., for Let's Encrypt this would be < 30 days), or less than 10 days of validity remain, whichever occurs first.
The dashboard will show you when to expect renewal if you hover your mouse over the "Remaining" colored bar on the Dashboard.
In the future I plan to implement the ACME ARI spec which allows servers to suggest when to renew, but the spec isn't finalized yet.
