I've been seeing posts like these from WordPress support staff.
Nov 6, 2013, 7:06 AM
The information you found on our support forums is out of date — since that post was made, Squarespace has changed their instructions for pointing domains to Squarespace. Our domain manager does not include a domain forwarding option like the one Squarespace currently recommends.
I went ahead and entered the DNS records you need to point your domain to Squarespace. I also entered the records you need to keep your email working with your custom domain. (Please note it can take up to 72 hours for changes like this to take full effect.)
Please let me know if I can help with anything else!"