can anyone link me a site where I can find when GLD diff should be changing
No, such info is not available.
You can only check when the diff has changed on a website or two.
I list the current diffs for all coins on my site (
www.WhereToMine.com), but not when they are changing (that would probably be good to add!) ... I'll make a note of that and see if I can add that. I just started the site last week, so I'm always looking for good suggestions on how to make it better.