To help handle the load, the site for non-logged-in users is cached, but will refresh every hour. So new posts will be delayed slightly from being shown.
For logged-in users, there is no caching, so you will see everything as it is posted.
You can stay logged in for 30 days before the session will expire.
@Robin On Chrome, for me, it keeps me logged in even when the tab is closed, so possibly third-party software could be logging you out.
Thanks,
Callum