I often see this error:
"Your session has timed out. Please log in again"
It is a large red error box, and it looks like something is wrong or I've done something wrong, but I haven't. I've just started my day as normal and started to try and do things.
At the very least this should be an info box, not an error box. But also if some reasonable time period has passed then it should just not show anything, it should be identical to if you didn't have any cookies at all.