There is a common property in Nintex Workflow called Current Time. This is actually something inherited from SharePoint. There are also two other item properties to do with time, Created and Modified. All of these properties only give you the hours and minutes for the time, not the number of seconds. Sometimes, the seconds are needed. This is where you needed to start thinking outside the box.
Nintex Workflow is an extremely flexible product. There are a large number of actions that come with it. Some of these can be used for thing that they aren't intended for. The best example is the Execute SQL action.
SQL is a powerful language and can do things that aren't specific to database queries. In the case of getting the current time, including seconds we can run a very simply query.
This will return you the current date and time, including seconds. Then you need to parse the data and pull out the seconds. I've put that into the UDA that can be downloaded at the bottom of this post.
Extract data between two text strings
What I was hoping to show here briefly, is the ability to do all sorts of things with Nintex Workflow that may not be obvious. To end this, one other action that is similarly flexible, is the Call Web Service action. There are so many web services out there, that the number of things you can do is limited only by the imagination.