Does increasing timeout increase your number of concurrent sessions?
Release : 17.3
Increasing timeout setting will not increase the number of concurrent sessions if the end users log out after usage.
However, if the end users simply close the browser instead of log out, then yes most likely you will see some bigger number in concurrent sessions as it will take a longer time for Service Desk to time out those "orphaned" sessions.
Bottom line, end users should log out of the SDM UI instead of simply closing the browser.