During ramp down phase, users are marked for ramp down (exiting state) as per the ramp down phase settings. For example, if total users are 100 and ramp down is 1 user every 10 seconds, then one user will be marked for ramp down every 10 seconds. Once virtual user is marked for ramp down, its current session will be handled based on the ramp down settings.
Ramp Down Settings Options
Allow current sessions to complete
Current session of virtual user will be completed before user is removed. User will be allowed to complete remainder of the session of given time (default 5 minutes). If test schedule is for sessions, then maximum time will not be applicable.
Use normal Think Times : Think time is used as per configuration and session is completed.
Disable all future Think Times : All future think times are disabled, all steps are executed and the session is completed.
Hasten completion by disregarding all Think Times : Current (if any) and all future think times are disabled. All steps are executed and the session is completed.
Hasten completion by disregarding all Think Times and use no activity timeout : Current (if any) and all future think times are disabled. All steps are executed and the session is completed. Also no activity timeout is used as per the input given. For example, if no activity timeout is given as 1s, then if any response not coming in 1s, step will timeout.
Stop session after current step (like web URL) is complete
Current session is stopped immediately or after completion of current step (if any) like hitting web URL. Remaining transactions are not hit for the session
User configured no activity timeout : Configured no activity timeout settings are used.
Hasten completion by using no activity timeout : Use no activity timeout setting given with this mode to hasten the complettin of current step.
Stop session immediately
Current session is stopped immediately. Current step (if any) and transaction is ended with status "Stopped" and remaining transactions are not hit for the session. Session status is set to "Stopped".
Notes :

1. No activity timeout can be configured from "Group settings > Protocol settings > HTTP > HTTP Timeout"
2. When the duration is given in iterations and Rampdown settings is "allow current session to complete", then maximum time will not be applicable unless you stopped the test.
3. When the duration is given in iterations, as soon as the last iteration started then the virtual user is marked as ramp down. (exiting state)

Runtime Changeable No