After you sign-up, please follow the steps below to Quantify your Squarespace site:
1. Log-in to Squarespace and navigate to Settings.
3. Enter your Quantcast tag and click Save to complete the process.
4. You’re done!
Once the tag has been implemented and you’ve submitted your sites, Quantcast takes 1-2 days to verify your site. After your site has been verified, it can take up to 4-6 days for traffic graphs to display.
For more information from Squarespace, please visit their resource here.