I've noticed that this question was asked a few times in the sticky threads up above with no answer. I also searched the BBB and could find no indication what kind of action it uses, or any explicit reference to hit limits (to the boost or the duration), or even an explaination of if the Combat Turn you activate on counts towards the total Combat Turns.

So i fired off an email to info(at)shadowrunrpg.com. So far it seems answers come in a 2 to 3 business day turn around, which is pretty good. I'll let you know how it turns out, i asked permission to copy/paste the answer here.

EDIT: I hate it when i make a spelling mistake in a thread title.