If you use your back/forward buttons to navigate, that could cause unwanted cookie changes. If you can, try and use the internal links at the tops of the thread pages to navigate between threads/posts; they don't cause as much havoc with the cookies.

As far as viewing posts from a certain time frame forward, there's a dropdown at the top of each forum that allows you to view posts from a certain amount of days forward. Unfortunately, there isn't an hour setting there.