mixmkr,
I believe it's based on when you register Melodyne Essential. If I remember right, the process goes like this:
1. Install and activate X3.
2. When you try to use Melodyne Essential in X3, it will prompt you for the Melodyne serial number.
3. When you input the Melodyne serial number, it will then guide you through the registration process.
4. During that process, you will be asked if you want to upgrade to Editor for $150.
5. If you select No, they will send you an email with the same upgrade offer, and you will have 15 days to decide.