MyLeadSystemPRO should only log you out of your membership backoffice after 20 minutes of inactivity (no page changes), sometimes sooner depending on the server.
We recommend when working on something for quite a while, and have not changed pages, saved, or reloaded... please be sure to copy your work and paste it into Word or a text editing program. Save your changes there... then you can go ahead and try saving on the site. In this way, if your session has timed out, you will still have the body of your work saved as a backup... which you can then just copy and paste back in.