#1 - You need to look for trains from Napoli Centrale (NA C.LE) not from Pompeii

#2 - There isn't a direct train, you must change (usually at Caserta but there are other options)

#3 - It is usually about 5 hour train ride. Going overnight means you leave Naples at 10:30 pm, arrive in Caserta at 11:30 pm and then wait in Caserta for a train that stops there at 2:45 am, arriving in Lecce at 8:22

#4 - As an alternative, you could leave Naples at 4:15 pm, arrive in Caserta 5:00 pm, then change to the EuroStar that departs Caserta at 5:20 pm and arrives in Lecce at 9:50 pm -which will put you in Lecce just in time for dinner.