When do we land?
at-ter-RIA-mo — stress on third syllable. The double 'r' and double 't' are both held briefly.
During the flight when you want to know the estimated arrival time.
'Atterriamo' is the first person plural of 'atterrare' (to land), making it 'when do we land'. This is a complete, natural question. The flight information is usually announced by the pilot and visible on the seat-back screen as 'ETA' (estimated time of arrival).
A che ora arriviamo a destinazione?
What time do we arrive at the destination?
More precise — asking for local time at destination
Quanto manca all'atterraggio?
How long until landing?
'Quanto manca' = how long is left. 'Atterraggio' is the noun for landing
Siamo in anticipo o in ritardo?
Are we early or late?
Compare current status to scheduled arrival
Italian pilots (comandante) typically make announcements in Italian and English. They give cruising altitude, outside temperature, local time at destination, and estimated arrival. On ITA Airways flights, the pilot's announcement style tends to be formal and brief compared to the chattier style of some low-cost carriers.