The quote expiry date is controlled by the number of days the quote is allowed to expire after.
The maximum value is controlled by the developer as agreed with your business.
The number of days can be changed up until the quote is sent, which fixes the expiry date.
When a quote has been sent, the expiry cannot be altered and is locked to the date the quote was sent.
If a quote has expired then an order cannot be received against it and so it must be cloned and re-quoted.