countdownStartDateTime property
Wall-clock time the verification code was issued at, used as the countdown anchor.
When null, the countdown is not shown and the field stays in its
active state indefinitely. When set (and showCountdown is true), a
countdown of countdownDuration runs from this timestamp; while it is
running the remaining time is displayed below the digits, and once it
reaches zero the field switches to the "code expired" view with the
onExpiredGoBack button.
Implementation
final DateTime? countdownStartDateTime;