Unfortunately, you will need to read Dutch to understand this, but it is perhaps a little more detailed: http://www.gvb.nl/reizigers/kaartjek...velTicket.aspx

For the part that concerns you, it says that there are two single ride train tickets and a GVB ticket (for the number of days you select) that you throw away when you leave. It also says that this card is ONLY available at the airport at a booth called "Holland Tourist Information" that is opposite arrival hall number 2.

To be clear: it is two different kinds of tickets. You cannot use one ticket for the other type of transport. The 24-hour ticket for the GVB is not acceptable for the train and, if a conductor asks for your ticket and you show him or her your GVB card, it will be the same as saying you have no ticket. The only way to start the hours is to use the card to check in a tram, bus or metro. You cannot start the hours on the train.