As you could not configure the server itself, I would assume it is not possible for cloud customers.
I also could not find anything in the documentation: https://confluence.atlassian.com/display/Cloud/Confluence+Cloud
Do you mean user session timeout (timeout = time to automatically log out the user if the session is idle)?
I do afraid it is not possible for confluence cloud, and for JIRA cloud they have an open issue: https://jira.atlassian.com/browse/JRA-34258
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