NO-but on a pass this is NOT possible-you can only use 2 days in your own country and I guess 1 has been used for to go out of that hexagone. But you did not state that clearly. (Day 1: lve Nice, day 2: TGV to Natnes)

These tips OUT and IN can also be sued to go to aiprot or seaport, and Nice has the 2nd airp of la douce france (maintenant pas de gréves?)

This is not true. It can be possible with the night train to use 1 travel day on the return trip if you board the train in Paris before midnight there will be no new travel day used after midnight. 

 @Aline Blot Can you please write the travel details (departure time and route) of the trains that you want to take in France and to/from France. The you will get a correct answer.

Dans les FAQ j’ai vu la réponse pour les trains de nuit et le décompte des jours mais je ne sais pas si j’ai le droit de prendre un train de nuit avec un départ dans mon pays de résidence??

voici le détail.

Départ le 26 juillet Nantes - Khel - OUT

Retour idéalement le 8 aout NIce- Paris en train de nuit (départ 19h16 arrivée à 7h55 Paris) - IN

OU je peux aussi partir de la frontière Italienne Vintimille à 17h22 - Nice 18h23 puis train de Nuit si je dois absolument partir d’un autre pays que le mien pour valider mon IN

Puis Paris Nantes le 9 aout dans la matinée.

Bonne journée à vous

You can only board train in France on 2 different dates so if you leave France on the 26/7 then you can use one more travel day in France. 

Going from Nice to Paris on the 8/8 and then from Paris to Nantes 9/8 will not work as you will board trains in France on 2 more days.

Merci pour votre réponses.

Vous me confirmer donc que j ai donc le droit de faire Nice Paris le 8 août en voyage retour et que je ne suis pas obligé de partir d Italie pour valider ce voyage. 

Bonne soirée 

You don't need to leave Italy or any other foreign country to use your inbound travel day. You can travel to/from an airport or harbour if you like.

You can use your Interrail Global Pass in your own country during two travel days of your choice for one outbound trip (leaving your own country) and one inbound trip (entering your own country). 

You can take as many trains as necessary to complete these journeys, but you are not allowed to make any extra trips within your own country. You can also use them in the order you prefer (that is, you may use the inbound trip before using the outbound one if that better suits your travel plans). You can read this page for more details