You have x days to establish an internet connection

When using a single user subscription product  it will perioidcally check that your license is still valid i.e. still assigned to you and not expired. If it can't communicate with the autodesk license servers ti will start a count down. If it reaches 0 your product will refuse to run.

This is the checklist you need to work through to see where the problem lies:

Solution:

If your computer is not connected to the Internet, connect it and launch your Autodesk software to validate your license.

If your computer is connected to the Internet and you receive this error, try the following solutions to establish an Internet connection.

• Solution 1: Correct inaccurate local system time settings​
• Solution 2: Check Internet security settings 
• Solution 3: Allow access through a proxy server
• Solution 4: Check LAN settings in Internet Properties Connections tab
• Solution 5: Verify that firewall security settings aren't blocking access
• Solution 6: Regenerate compromised root certificates and verify that Certificate revocation check is not disabled by your GPO. 
• Solution 7:Standard users - Request your administrators to provide full control to registry keys and folders Autodesk products use. What user permissions does AutoCAD require?

To troubleshoot this issue for a macOS product, see Error: "Establish an Internet Connection to Continue" on macOS.