Originally Posted by Perche

Depending on the lines and time of day, it can take 30 minutes or more to get through passport control. Then, 15-20 minutes to get to the Malpensa Express and buy your ticket, depending on the lines at the machine or booth. Then, up to 20 minutes waiting for the train to Milano Centrale. Then, about 45 minutes to get to Centrale, and 20 minutes or more to find your train and get on. Then, leave yourself about 30 minute cushion. So, I'd say about 2 hours to be safe.

On the other hand, are you sure you want to do that? Sometimes, there are big savings booking in advance. Other times, and advance ticket is the same price as a walk up ticket from the machines 15 minutes before the flight. If you have already purchase a ticket, and you are delayed and miss your ticket, you will have thrown out over 100 euros per ticket. Often I'll wait, and buy them at the train station. This way there's no added stress if my flight is delayed, if I get lost, if I want to stop for a cafe' or glass of wine, etc.

For example, right now Trenitalia is showing 109 euros for a business class ticket for this route today. It's showing the same price for this route one month from now, so you're not saving anything by locking yourself into purchasing a specific seat on a specific train by buying it before you get to the station.

For the same route tomorrow and one month from now on Executive Class (It's not called first and second class on this train, it's Business and Executive) it is 209 euros. Frankly, the difference between Business and Executive is negligible, and not worth the extra 100 euros unless you are on an expense account. The seat is marginally wider, slightly more cushioned, and with slightly better leather, but it's hardly noticeable. It's certainly not worth an extra 100 euros per ticket.