Hmm. You can wait the 24 hours for the actual link. But I followed these instructions to complete my secondary,
“If you do not receive email instruction within 24 hours after this notification, please visit
https://explore.acheedu.org/, complete the form using the email address on your AACOMAS application and following the instructions. Once logged in, you should see a "Secondary Application" link on the left.”
If that doesn’t work, I’d call and ask for them to email the link. They are very nice. The secondary is REALLY important here because that means you’re pretty much getting an II. I got my II the next business day after submitting. But only after I completed the secondary AND completed the technical standards pdf.