We booked a return ferry from Livorno to Bastia, mid June:
8am -12:30 pm: in reality it left only at 08:30 am, but arrived around 2:30pm, so it took 6 Hours instead of 4,5h
Not even considering the time it takes to get off the ferry!
Embarking process inside the ferry was pure chaos, cars were parked every which way to jam in as many cars in as possible, leaving no space to get out or get back in.

Apart from a single shouting staff member during parking, all staff were friendly and kind.
Food on board was fairly expensive, but good quality. Plenty of seating, never too crowded. Wifi does not work.

Return: 2pm - 6:30pm
Reality: 3:15pm - 9:15pm
Considering the time before embarking and getting off the boat, the whole journey took around 9 hours, so we wish we had known that to better plan the rest of our journey.