How far is the Astoria Garden Hotel from the Rome airport?
It takes you about ten minutes from the hotel to Termini station (by foot), where you will walk another five minutes until you reach the platform where the Leonardo Express departs. The train takes about 40 minutes, and you will have to walk about five to ten minutes within the airport. So it should be safe to plan about 90 minutes for your journey (remember that you may have to wait a few minutes for the train!).