Expires is a String property that represents the optional Cookie attribute that defines the valid life time of a Cookie. Once the expiration date has been reached, the cookie will no longer be stored or given out. 

Expires is expressed in a format based on RFC 822, RFC 850, RFC 1036, RFC 1123, and RC 2822 with the variations that the only legal time zone is GMT and the separators between the elements of the date must be dashes. For example: 

   Wed, 04-Jul-2001 01:00:01 GMT

When Expires is omitted, the Cookie will expire when the HTTP session ends. 

There is a bug in Netscape Navigator version 1.1 and earlier. Only Cookies whose Path attribute is set explicitly to "/" will be properly saved between sessions if they have an Expires attribute value.

TIdNetscapeCookie.Path