well, i think you have to be very early in SFAX TRAIN STATION because the fisrt departure is at 2:10 night which arrives to TUNIS at 5:55(it takes about 4 hours).
i've looked for another time but it seems that doesn't work just because the second train is at 5:25 which arrives at 9:15 am, so you could not reach your appointement.
i think you will have to be early as i said to you before 2:00 night to buy your ticket and have your place.
good luck.
