increase the amount of time it takes for a headspider to take over

[Mordent]

I think you got to weigh out the possibilities. Which are, "Do I follow the law and try and save one human" or "Will trying to save this human result in other humans dying"

If a traitor tells you (a mediborg) to heal them (and they are still human) you are required to attempt to do so, even if they're still going to cause trouble the moment they're healed. Humans are humans. You get to prioritize, but you don't get to deny requests by humans to help them (assuming no other laws get in the way). I'm going to pre-emptively state that while Law 2 doesn't apply if it would contradict Law 1, you have no control over the actions of the human - if you're going with the "I cannot save you because you're going to harm humans, so Law 1 prevents me from doing it" logic, that really doesn't hold imo. If it did, you could stretch it well beyond that line ("AI, tell me where so-and-so is", "I can't because you might harm him").

A borg should always kill non-humans and an argument could be made that once they get headspidered that they are no longer human at that point.

I strongly disagree with the first part of that sentence, and would personally disagree with the second. They're human until the changeling takes control, and you can't prove definitively when that is.