Why PHPUnit tests run faster when the machine is disconnected from the internet?

I have noticed that when my laptop is connected to the internet my PHPUnit tests takes between ~90 sec ~200 sec to finish. But when I disconnect it from the internet it runs in less than 20 sec!! that makes me happy and sad at the same time!

In both cases all the tests are passing, I'm sure I'm mocking every request to external API's.

Is this something related to PHPUnit or to my code!! any one has an idea on what's going on. Thanks