Rezzing an installed asset or upgrade as the Corp never costs you a click. You pay a click to install it, but rezzing can be done any time specified in the timing chart (usually in between actions). You can rez PAD Campaign after the Runner's 4th click before your turn starts
You can also rez PAD Campaign at the beginning of your turn in step 1.1 of Corp's turn and still get the credit. "When your turn begins" conditionals trigger at step 1.2. This was updated in the FAQ and is not like this in the core rule book.