Hi @olivier T,
Please find attached a sample model (entry-and-exit-times-for-1-processor.fsm😞

The Statistics Collector listens to 2 events on the Processor:

For both events, I renamed the label name of the entering / exiting simply as item:

This label name is then used in the Data Recording tab to create unique rows for each item:

The Object and EntryTime columns are updated when a new row is added in the statistic collector:

And the ExitTime column is updated by event dependency:

This column's data is updated only when On Exit is fired:

As a bonus, I attach another sample model (entry-and-exit-times-for-a-group-of-processors.fsm) if you want to to track the entry and exit times for a group of processors:

Hope this helps.