Don't must of these services (Skype, Facebook, WhatsApp), load the URL to fetch a thumbnail, page title, and page description, to show in the chat window instead of just the URL?
just compare the time the message was opened on the target client with the server-hit(s) for that URL..
The content is encrypted between you and the receiver. If you didn't hit the URL and the recipient didn't hit the URL, how did someone else hit the URL which was encrypted in the transmission?
In whatsapp the URL is hit before you send the message, you can see the image/title/description pop up when you paste a link