Currently, you can enable and customize Idle Timeout settings for learners (or disable it altogether) in the Portal Settings.
There is no similar setting for admins. While I understand this may be due to the level of damage someone could cause logged in as an Admin, you should at least be able to set the Idle time for admins.
I'm not sure if it's due to our SSO integration or not, but these idle timeout logouts often don't resolve themselves well - I'll find I'm on a blank dashboard page (where it asks me to add a dashboard), or a system request just spins and spins - only to find out that I've exceeded the timeout and I have log back in.