Tokyo Metro 2-Day Open Ticket

If I buy Tokyo Metro 2-Day Open Ticket special for tourists sold at Narita Airport.Could I specify beginning date to activate the ticket?Or I have to use it on that day.
Thank you

as far as I KNOW the Tokyo METRO 1 day or 2 days open ticket get automatically activated when you first put it in the turnstile(don't forget to take it back!)
this has been my experience with similar tickets/passes in several towns in Japan but also in other countries. By the way the Tokyo 1 or 2 day Metro ticket is only good for 8 of the 12 metro lines in Tokyo. Check on this site for more details( enter you question in the small window above all the questions to get a list of previous posts on the subject)

Thank you very much for your kindness.I wonder if there is a difference between 1 and 2 day open ticket sold in town and those sold in Narita Airport. Because the cheaper one can only buy at the airport.So for my 4 days trip I will buy 2 of two days open tickets and use them for my 1st ,2nd and 3rd, 4th day consecutively.

I may be totally wrong but
the only difference I can see is that the tickets sold in Narita are for foreign tourists only and, because they are cheaper than the regular ones, is an incentive for foreign tourists to go all over Tokyo and, possibly, spend their money in various neighbourhoods rather than in the same few well known areas. This is only my opinion but
I think that this is also the reason why the all Japan JR pass(for foreign tourists only)is such a good bargain (compared to long distance individual tickets): because travel to far-away places is so cheap foreign tourists travel all across Japan and spend their money in towns all over the country instead of staying in the same few big towns only, which they would do if travel was much more expensive. It is win-win for all. I may be totally wrong but I am making this assumption by comparing with, for example, the French railway pass that, for the same price as the JR 7 days pass, only gives 4 days (though they can be spread within one month).

There are two differences between the regular and the tourist version:

1) Price: the tourist version is cheaper
2) The 2-day pass is only available as a tourist version. There is no 2-day pass available in Tokyo itself.

Also, it is not true that the tourist version is for foreign tourists only. It can be purchased by anybody, including foreign residents of Japan and Japanese nationals.