When you modify an open timeslot, depending on the modification, the timeslot might split into two separate timeslots.
A timeslot splits when:
You stop a run and select to keep the reserved resources for the remaining time (for performance test timeslots only).
The run ends more than 30 minutes before the timeslot ends (for performance test timeslots that are not "NEW" ad-hoc timeslots).
You modify an open timeslot that is not active, that is, no tests are currently running.
Note: When a performance test is running, the timeslot can be modified from within the tests' Test Run Page only. Changes that can be made include: prolonging a timeslot, adding Vusers, and adding hosts. For details, see the Performance Center documentation.