Thank you for your inquiry @aya_zaki. The short answer to your question is that the license starts at the date of download, not the date you first run the software.
The full process is as follows: To download a product evaluation from the Lumerical downloads site, you first need to register in order to create an account. The registration process typically comprises of two parts. The first part prompts you to enter general information, including a valid email address (such as one provided from an employer or school). You should then receive an automated confirmation shortly after, sent to the email address provided. This message will provide a link to validate the account and complete the final step of the registration process.
Completing the registration will allow you to access the product evaluation portion of the download page. After completing the product evaluation form, you will be directed to download the product installation package. At the same time, the website will send another email with the license activation code. The 30 days starts as soon as this email is sent, regardless of whether the software is actually used or not.