The call for speakers usually goes out in July for the spring conference, with the application deadline typically falling sometime in August.
(At least based on my highly scientific method of searching through years of old emails - there are occasional benefits to being a digital pack rat!

)
You'll receive an email from
conferences@aapc.com, and AAPC will usually share it across their social media channels as well. Once it hits LinkedIn, you'll likely see it shared quite a bit, especially by NAB members and other active AAPC posters. If you're connected on any of those platforms, it's pretty hard to miss.
If I remember once I see the announcement come out, I'll come back and post the application link here in the forums, too! Just to make sure no one misses the information.