The length of a logged in session for a member is not directly controlled by WishList Member. WishList Member uses the WordPress login functionality (this is what allows a member to login using any WordPress or WishList Member login option).
So WishList Member does not determine the length of a user/member session once they have logged in as that is controlled by WordPress.
If you are interested in adjusting the length of the user/member session once they login, you can look into available options for your WordPress site or other plugins to accomplish that.
A Google search for a phrase like “login session length WordPress” will provide more info on this topic.
You can also check out the WordPress Plugins directory for potential plugins that allow for adjustments to the session length functionality.