When are imports loaded?

[MuntyScruntfundle]

If I have code that imports a couple of libraries I've put together, do they load to memory when the main thread starts, or when there is an actual call to the library?

Reason for asking, .I run my code and the app starts quickly, but there is a quite a pause when the libraries are first actioned.

So if I want an immediate response every time I call a library I have to make a dummy call before my processing actually begins.

Is this correct, or am I missing something about the import commands?

Thanks.