We send out a newsletter in Civimail, with links to our main website which is a different domain. We are using 'track click throughs' so the link, when clicked, goes via Civi first. However, the links seem to be expiring fast - I sent a test last night and the links worked fine when I received the email. But 10 hours later clicking a link just takes me into Civi, and not to the main website. What is the default timeout and can it be changed? We are on 4.6.12 and this is a Drupal site.