Molting is not the same for every species of bird, and even differs from bird to bird. The season of the year, the temperature of the environment, nutrition, and egg laying play a significant role in determining when a bird will molt as well as how long it will take to complete a molt. All birds molt at least once a year and this process normally does not affect their ability to fly. Some may even molt up to three times per year. For Amazons, molting seems to be a continuous yearlong process.
For more information, please read Molting in Birds