Sorry, I haven't been able to find anything like last log-in date/time either.
Have you tried using the "Mark Forum Reads" button? When you are done reading a forum, click on that button (in the top light blue menu bar). Then the next time you log-in only "new" threads/posts will be bolded.
And when viewing a forum list, there is a little blue dot between the avatar and the title -- someone said it's an eye but looks like a blue dot to me -- for threads with new posts. If you click that dot you'll go directly to the first new post in that thread. Though I seem to go to the first new post anyway even when I click on the thread title. You can also click on "Go to First Unread" below the title at the top of a thread if it doesn't happen to pop you to that spot automatically.
HTH!