The ideal session time out is 2 hours, as far as I know. Apart from this, Adobe would also log out the session in case the IP changes dynamically in between. This is due to security reasons. Please refer this doc: Troubleshoot expired sessions in Adobe Analytics and reach out to Adobe Client Care with all the IP ranges to whitelist them. It might help significantly.
I don't have a solution but just highlighting that I am also having the same issue, I get logged out whilst building up reports and dashboards and am losing hours of work as it does not automatically save work.
Other than constantly saving work every 5 minutes, is there a better way to get round this.