We assume you need to adjust HTTP session timeout - timeout when you do nothing in SAP ME and SAP ME keeps you logged in. When session expires, you need to login again. By default, this session timeout is set to 30 min, but can be modified.
You can check/modify timeout in Netweaver Administrator -> Configuration Management -> Infrastructure -> Application Modules. Find Web Module called "manufacturing", and below, in Web Module Details, go to Context tab. There is a Session Timeout parameter, it is 30 by default, though you can try and change it to something else (e.g. for manufacturing-services it is set to 60 by default).