Koya-San World Heritage Ticket Validity

I know questions about this ticket have been asked many times before, but none of them have answered a question of mine with enough clarity. I am planning on doing the one night "pilgrimage" to Koya-San and was going to purchase the ticket for the convenience, and to save the few yen it actually discounts. I wanted to buy it on a day that I had some time free in Osaka, say the 16-Dec, but I don't want to use it until 18-Dec and 19-Dec. Is the ticket valid from the date of purchase or the date it is first used? I want to do this because I will be on an early train from Osaka to Koya-San to make the most of my day (planning a lot of walking) and was sure that the ticket office wouldn't be open on the morning I head up to the mountain. Thanks

According to the website below, it says Koyasan World Heritage Ticket can be purchased one month before the actual departure date.
http://guesthouse-hostel.com/hyogo-osaka-to-koyasan-ticket/

So you can designate the date of activation when you buy the ticket at the station.

Thank you very much for that!