John,
Just to chime in, here’s a helpful link:
https://atpflightschool.com/faqs/acpp-prep-written-knowledge-tests.html
The test results are valid for 24 calendar months. So, starting now will be just fine.
I would get as many of them done as possible. Don’t worry about your orals just yet. The writtens are more of a formality. You will have plenty of time to prep for your orals while in the program.
Here’s another helpful link:
https://airlinepilot.life/t/what-does-an-atp-student-need-to-do-to-be-successful/10421/5
Tory