Practically seen it is instant. But to be sure the transaction cannot be reversed a number of “confirmations” need to take place on the network. On average the transactions are confirmed within 3 minutes. Confirmations are acknowledgments that your transaction have been seen by other users in the network. Transactions that are processed via nocks.co are confirmed within one second. This can be a purchase using your app, online or in a bricks and mortar store, paying the merchant in Gulden or Bitcoin.
With the upcoming developments it will no longer be needed to wait for the so called confirmations. The Gulden protocol will be adjusted in such a way that you will need “zero confirmations”. For more information about the upcoming developments see: https://developer.gulden.com/roadmap/
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