ChilliDB holds login sessions open for 240 minutes, 4 hours, by default. This is to ensure that if you are called away from your desk or move onto another task while working in ChilliDB, any unsaved changes can still be applied for a reasonable amount of time.
The downside of this, is that if your system is low on User Licenses available, some users will not be able to login.
It is a balance you can configure by adjusting the Idle Timeout to suit your usage patterns.
You can adjust this yourself through System menu > System Management > Manage, then choose Manage System Configuration. You can then find the setting System Session Idle Timeout and configure it to a number of minutes.