When should garlic be added to the pan to get maximum pungency?
Garlic's pungency is released by cutting it.  The more finely the garlic is cut-up, the stronger its taste will be.  So minced garlic will be stronger than chopped garlic.  Chopped garlic will be stronger than sliced garlic.  Etc.

Cooking mellows the sharp pungency of garlic.  More cooking - milder flavor.

In order for garlic flavor to be strongest, you should mince the garlic and cook it briefly.  Assuming you are trying to flavor vegetables, you should add your minced garlic shortly before they are cooked to the point where they ready to be served - give the garlic 30 seconds or so.