You also have immigration to get through. Where are you flying from, and who with? They all make a difference. Last year I went back to Europe for a trip using Iberia when I returned to BA - It rook an hour plus to get thru immigration (lots of EU passport holders). This year I went home via the US, and arrived back in BA on a US Carrier, and as an EU passport holder, I was thru immigration in less than a minute, as all the US arrivees were being seperated and made to pay their "Welcome" tax.
So, as Jez says, there are a lot of variables to consider before an homest answer can be given. In general, you should leave an hour to get thru the airport, and if you have a car booked, maybe 30 minutes to palermo - If you have to wait for a taxi, ro organise one when you get here, maybe another hour.
Maybe the best thing to do is get a taxi to Palermo, go to a cafe/bar, relax, have a drink, call your landlord, and arrange to meet him/her now you are arrived in Palermo.