The starting and peak number of virtual users in LoadStorm represent concurrent users or the number of simulated users at a particular point in time. Each concurrent user will last for the duration of the script. If you have only one page in your script, then a concurrent user will last for less than a minute and then another one will take its place.
For example, if you have a test with one script having one page, starting at 10 concurrent users and peak of 10 concurrent users for 20 minutes, there will be 200-300 total users simulated (and same number of sessions). LoadStorm will create a new session for each virtual user, but it will not maintain the session after the script has ended, so your session should time out as you have configured it.
The LoadStorm test parameters simulate “concurrent” users not total users. The total simulated users will generally be much higher than concurrent users, but the actual count depends on lots of other factors such as the number of pages in the script, think times, etc.