I kept having the issue last week, it wasn't based on any times. It logged me out two or three times in one day. And I never touched my SSC cookies.
I also had pretty bad issues with posts not appearing last week. I'd get an email about a reply to a post, click the link, no reply seen - just my last post. I'd see the user and time as the last post when looking at the forum thread list, click that to get the last reply, post not there. I'd try with a different browser and not logging in, I could see the last reply and time in the list of the threads, click on the time to get that last reply and it wasn't there. Click on the thread and only see my post as the last one. I timed it just two or three times and the post would show up 20 or 30 minutes later - with the correct time of 20 or 30 minutes earlier. Just seems like something very odd was going on last week.