Immediately after a message is received, it remains in the queue. To prevent other consumers from processing the message again, Amazon SQS sets a visibility timeout, a period of time during which Amazon SQS prevents other consumers from receiving and processing the message. The default visibility timeout for a message is 30 seconds. The maximum is 12 hours.
Message retention defaults to 4 days and a maximum of 14 days – although it is defined in seconds.
There is also a delay queue by setting a delay value greater than zero / 0. The default is zero, there is no delay.
To delete a message from the queue a receipt handle is required – in addition to authority to delete it – which is usually the case if you can read it.
On message queue polling – long polling is strongly preferred as short polling (spinning on the queue) can consume large amounts of CPU / resource. The max and default long poll is 20 seconds.