Some of the recipes we undertake will often mean that we start the work in some part of the Joomla! control panel and then leave it partly done while reading further or perhaps gathering information elsewhere. Joomla!, in an effort to be helpful and secure, will log us out after 15 minutes.
I would suggest that changing this session lifetime to 60 minutes is sufficient to virtually always avoid entering loads of data, only to have that data wiped because we hadn't saved it yet and Joomla! logged us out.
Log in to your Joomla! control panel using the username and password you chose in the first recipe: