Auto Log Out

Is there any way to declare how long you want to be logged in for (as there is on ProForums)?

Twice now, while composing a message, when I hit submit I am returned with "you are logged out" while I was typing.

The first time was my first ever thread/post. So much typing had disappeared! I banged my fist so hard on the desk that I hurt it and had to retype the entire lot. Since then I learned to copy the text before pressing submit, log in again, hunt down the thread again, and paste it in.

What is the default log-in time? It seems to be about 20 minutes.

(copies this text before pressing submit.......)