How long what? If you're asking about the wait for a table, Ristorante di Canaletto currently shows 20 min and Magellan's is 40+ minutes in the TDR app (3PM on Saturday). If you're asking about how long a meal takes, it'll depend on how quickly you eat. They're quite fast at serving dishes so you can comfortably finish a meal at Ristorante di Canaletto within 45 minutes and a meal at Magellan's within an hour. You can also take your time and eat for 90 minutes if you want.