Session invalidation time is someting the slack admin (That is, EA in this case) configures themself. Fun fact, if you want SSO for your Slack, you have to pay

Session invalidation time is someting the slack admin (That is, EA in this case) configures themself. Fun fact, if you want SSO for your Slack, you have to pay extra unless you are already using one of the top tier Slack editions. So either pay up, or have multiple ways of administering your users, with the security implications that causes.