It possible to add a Journey Log to a single leg of multi-leg trip.
In the example below you can see a screenshot of a Jorney log added to the first flight of the trip. To add a Journey Log to a specific leg, you need to mark the checkbox (flight) and fill in mandatory fields: flight times and fuel data.
Once the Journey Log is saved, this will be marked in Flights List as . All legs without added Jorney Log will still remain as .
You can see this clearly on the screenshot below.