Does it take all your initiative passes or just one?

Hacking on the fly is a Complex Action where you make a Hacking + Exploit (Firewall, 1 Initiative Pass) Extended Test.

So every initiative pass would require a new roll, thus hackers with more initiative passes can break in faster.

If the ruels say "An extended test using (Whatever + whatever) (Threshold) 1 combat turn" then yes, it takes the whole combat turn, regardless of passes. If it says "An extended test using (Whatever + whatever) (Threshold) 1 initiative pass", then you get to retest every pass. Pretty simple, really, though the wirters may not have followed their own procedure for test annotation.

The format is usually Skill + Attribute (Threshold, Interval) for extended tests. Attributes and skills can sometimes be substituted by programs, hardware, etc.

Yeah, Hence the "Whatever + Whatever"

I was just trying to clear up that the theshold and the interval are in the same set of parentheses, seperated by a comma.