Yes, you may log in before the PQ Program starts.
Yes! As soon as you receive your welcome email for the PQ Program, you should be able to log in to both the PQ app.
When logged in, you can use the PQ Gym, but the app-guided exercises will not unlock until Tuesday after your Program begins. (This is by design, as the first training session will provide more context and direction for your daily practice within the app.)
If you are unable to log in, please see this troubleshooting article.