Leash will always pop up windows with warnings that your tickets are about to expire, beginning 15 minutes before the time of expiration and continuing every 5 minutes. However, when this option is selected under the Options menu, a bell will ring as well.
When you view your tickets and tokens, those shown in yellow are due
to expire in less than 15 minutes; those in green have 15 minutes or
greater. (A red ticket is one you have but is expired; gray tickets are
not available to you at the current time, because Leash or your machine
is missing a requisite module or piece of functionality.)