The IResponse::get_Expires method retrieves the current value of the Expires property of the Response object.
HRESULT get_Expires( VARIANT * pvarExpiresMinutesRet //a pointer to a VARIANT that // receives the Expires value );
If the user returns to the same page before it expires, the cached version is displayed. If this property is set more than once on a page, the shortest time is used.
Response Object, IResponse::put_Expires