Apologies for this off-topic post, but there's nowhere better to ask than this forum, with its many HKG experts!

From http://www.mtr.com.hk/eng/train/ae_tourtickete.htm , I learn about two MTR special passes: 1) A 1-day MTR pass good for 24 hours from time of first use. 2) A tourist pass good for one or two single Airport Express journeys, plus 3 days of MTR journey ("starting on day of your first MTR journey"), plus HKD20 credit towars other transports.

Pass #1 is very clear as to validity -- 24 hours from first use.

What about pass #2? Suppose I arrive HKG in the evening and take the Airport Express in to town. Suppose I don't use the ordinary MTR (as distinguished from Airport Express) until the next morning. Is my pass valid for 72 hours from that first use? Or does its 72 hours begin to toll when I get off the Airport Express in Central?

Or do I get three calendar days beginning when I get off the Airport Express in Central? Or three calendar days beginning with my first use on MTR? Under the "calendar day" rule, it's desirable to make sure the first day is a full day -- that is, to start using the 3-Day Tourist pass on a morning -- which is a perfectly typical constraint (e.g. other cities' subways have this rule), but so much the better if I don't have to think about this.

The rules in #1 are so precise, but #2 is still a bit unclear to me. The specifics make all the difference as to whether I should use

(In case it matters, I don't expect to have a connection beyond the end of the Airport Express line. But, incidentally, what if I did? With an Octopus card, I'd ordinarily get a free transfer to MTR, such that my 3 days of unlimited use of MTR shouldn't be triggered to start by the mere transfer from Airport Express. But maybe that's not how it will really work!...)