Wow how to get flamed in one easy post by asking a question to which you don't know the answer. Glad to see such helpul advice as "reconsider your career options".
for those who ask why would you need ankle weights...? - If you are wearing light, open-heel fins and therefore dive boots during the 800m mask fins and snorkel swim, the feet can become rather buoyant and this makes it a little more difficult to effect good propulsion.
Good snorkel fins (or at least, full-foot fins in general) tend to be effective during the snorkel swim, mostly because you're not wearing the booties, so it's easier to keep your fins underwater rather than flapping away at the surface. It doesn't matter how great your technique is; if the laws of physics say your feet will float, then they will float.
I don't recall anybody asking to wear ankle weights during the 800m snorkel swim, and I don't think I'd be too concerned if they did. You can either swim or you can't and at the end of the day, when I'm evaluating DM swim tests then yes, it's great that people have good technique (applies to the 400m swim also), but even if they don't look so good doing it, what I'm looking for are people who can make the distance in a reasonably healthy time. The times required in the DM swim tests are not terribly challenging, but you need to be in reasonably good condition to do them, and all of my interns (myself included) did all 4 tests in the same morning.
To the question of would you have time to strap on ankle weights in an emergency? Why not? If they are in your kit box and close to hand when you respond, and you know you swim better wearing them, then the few seconds it will take to put them on might well be recovered by being able to swim to the victim faster. Just a thought.
Good luck with the swim.
Cheers
C.