Chronomancy doesn't break the 6th law unless you go back in time, unless the wardens are being jerks. Chronomancy for speed is still going forward, just slower.
Any power where you're able to generate a lot of offense risks breaking the first law...flash-level superspeed is certainly in that category.
But yeah, if you want to play Dr Who, you're best off playing somebody who is already a monster, not a half-breed, scion, emissary etc. In DFRPG though, expect your high concept and any other aspects to get a lot of compels...the whole point of mortals is they can change who they are. If you don't have a bit of mortal, it's going to be a pretty static character in a lot of ways, so you'll want to figure out what sort of thing you'll do when you hit milestones and whether you're comfortable with a character that reacts to shattering events by being more of who they already are. It's certainly doable, but it's a more alien character than most PC concepts.
(it's not like other genres don't have this problem, too, but the immutability of any being of the never-never compared to mortals is unusually strong in Dresdenverse. OTOH, there is some plasticity - Toot Toot is clearly changing into something more like a Sidhe, but most of the plasticity is seen as toxic...it's why the Denarians fell from being angels, it's a major plot point with the Ladies, etc).
While you can get some political protection if you belong to another faction, that's limited unless you BECOME that faction - while Elaine, if exposed as Justin's pupil, as Emissary of Summer wasn't going to have her head taken off by a warden until the political crisis was over, the moment she was merely a ward they'd have gone after her, it would have only been a matter of a death payment and they might have done it anyway.. Had Elaine been a changeling, similar. Had she been a changeling sorceress who became, say, a Selkie, or turned by the Red Court the Wardens would have no excuse at all to go after her, and likely wouldn't risk it unless they were at war with the nation.
Thing is though, the political protection if you're still mortal doesn't protect you from the universe. You'll still have to spend refresh on lawbreaker, although again, if I wanted to play a Time Lord, I'd likely WANT 3 refresh spent on 6th law. +3 to time travel stuff is right up their alley.