First of all: Welcome to the community.
Thank you
If I have understood everything correctly, your wizard/practitioner can/does only alter time where he and he alone is concerned, right? Compared with time travel this seems like a minor thing to me. He bends the flow of time around him and this more or less is only apparent to him? Cool idea!
Now: where the laws are concerned any kind of time magic automatically enters a very grey area of magic. Some things of the character concepts seem to be more greyish then others. The sixth law dictates: Don't swim against the currents of time. I'm quite sure when it comes to speeding up the time around your practitioner you are save. You are not exactly swimming against anything really, it's more like you are surfing on the currents. When it comes to slowing it down, now thats a horse of a different color and might be considered swimming against the current.
At least in my game the wardens would be very curious about these time manipulations and your guy would probably end up under constant supervision. I'm not talking "Doom of Damocles" here, it would be more like the council keeping an eye on Margret LeFey who danced around the edges of the laws all her life.
This doesn't have to be the case in your game though. All depends on what you and your group decide. If everybody is cool with your concept. No problems...
No, not when alone. In the same way how a vampire/half-turned would activate their speed. Course if the campaign involved stronger characters, I'd make his speed Mythic (-6), so it doesn't have to be a minor thing. As for the speed-downs, it's just the other side of the coin. He would sacrifice a few hours of his day to replenish some of the lost time the usage of his power would have taken from him. I think it would also lead to some possible plot situations as well. He's pretty much helpless in this state. If he's slowed down his own time, he can't instantly deactivate it if someone comes up to kill him. Someone could have broke into his house, stabbed him 12 times, robbed the place, and left before he would have time to react to the first bit (and of course die) and make time normal for him again.
And I feel the same with the warden's reaction. The character himself would be rather weary of letting anyone find out how he can do what he can to avoid the council looming over him. Since he has no evocation ability, he'd never be council material, so would at most be a member of the Paranet. And might lie, claiming to be a changeling or something so no one finds out (Course the sight might have him surrounded by clocks or something.) I think it would all rely on his actions with his abilities, on the consequences for them