IPhone : iOS GCD run tasks in different threads

Im writting an application to buy goods. I have GoodsViewController where is list of all products and PageContentViewController where user can buy goods. I need to set delay 3 seconds between action Buy on PageContentViewController and any action on GoodsViewController. Also I have AdminViewController where administrator can edit,add and delete goods. For adding used AddGoodsViewController and I need to set delay 5 seconds between action Add and any action on AdminViewController.

Accordingly, the action takes place in separate threads and during different operations can move to other screens and perform actions on them (even on the same screen to complete the current operation can start a new one). Updates screens should be in Realtime. How can I do this, or what I need to read to do this. If you can give me some code it would be great. Thanks!