5 hours is the default session timeout for JIRA user session. The session timeout in the plugin should be less than or equal to default session timeout.
You can follow the below steps to extend default session timeout:
1. Open <jira-installation folder>/atlassian-jira/WEB-INF/web.xml
2. Set value of session-timeout tag in minutes. By default its 300(5 hours). You can set it to 0 for unlimited session time.