The logout time is based on the server and the actual time differs but its normally around 30 minutes.
There are two options when storing data in a login based system like ours. Cookies or Sessions our system uses sessions.
A cookie can keep information in the user's browser until deleted. If a person has a login and password, this can be set as a cookie in their browser so they do not have to re-login to your website every time they visit. You can store almost anything in a browser cookie. The trouble is that a user can block cookies or delete them at any time. If, for example if the system's application utilized cookies, and a person had their browser set to block them, then they could not access the website ever.
Sessions are not reliant on the user allowing a cookie. They work instead like a token allowing access and passing information while the user has their browser open. The problem with sessions is that when you close your browser you also lose the session unless the user has saved the step of the application process.So by using a session it requires the user to login each time they visit the site which is ultimately the most secure option rather than using a cookie that wouldn't require them to login back in.
With sessions there is not a set time frame for auto logout its normally around 30 minutes or so but it differs from server to server based on configuration and its not something that can be changed globally or by user.
My suggestion would be to save your credentials in your browser so that each time you need to login its already typed in for you and all you need to do is click login.