Answer
The standard Duplicate command is deliberately scoped to just the one entity and won't cascade to child records — achieving cascading duplication requires a customization: add a new command that opens a dialog collecting whatever new values distinguish the copy (like a different employee or start/end time), then have that command call a custom projection action with a PL/SQL implementation that creates the new parent record and, if the source record has child records, creates matching copies of those too.