As early as you can in your add-in. Before you need to check whether the customer is allowed to use your app.
In step 6 of the following Wyday sample tutorial, you are creating the TurboActivate instance in the constructor of Form1.cs class. Where do we create such an instance in a VSTO project?
https://wyday.com/limelm/help/using-turboactivate-with-csharp/
As early as you can in your add-in. Before you need to check whether the customer is allowed to use your app.