This is a fun discussion. Time magic is one of my absolutely favorite areas of magic.
Low level chronomancy is likely fairly common, especially to minor talents. Most forms of precognition rely on it to some degree-for example, I Ching, Tarot, and other forms of sortilage, as well as astrology and it's ilk. Plus you have other talents, such as the woman in White Night who just saw a few seconds into the future all the time. It is more than likely that this character's presence would cause unusual side effects to any of these individuals attempting to use their powers, even if his power is localized within his own aura.
Because of the unusual nature of the character's magic, and his likely reputation as an eccentric/bad a$$, lesser practitioners may report the weirdo to the the Wardens out of principle. Even if he's a good guy (likely), super speed is usually confined to supernatural bad guys.
One thing that we certainly agree on is the detrimental effects that combat chronomancy has on a body. The first character that I have written up for the game uses a sickening combination of sensory chronomancy coupled with arithnomancy (I found a practical use for that weird harry potter stuff) to contain and calculate probable potential actions, and then wraps up with overclocking biomancy to achieve super speed combined with tactical superiority. This leads to a deadly opponent in combat, able to take on the monsters at or above their level physically, but leaves the wizard with torn muscles, stress fractures, lots of bruises, and possible minor brain damage.
If you built the character as a focused practitioner, it would give you more options to power the speed rather than just eating up your life. You could expand and contract time instead of spending it. For example, you compress the time that you need compressed so you get your speed boost, and later on you pay for it by letting time snap back into place, lengthening time around you when it won't get you killed, just make you really bored. But you run into the problem of external time magic, and the potential problems mentioned with that earlier. But you could use the ritual ability pay for your time in advance, sticking to your sanctum and waiting out the expanded time to limit potential effect on the outside world.
Think of the ritual as winding a spring or stretching a rubber band. You lock the potential energy into place for later use. With the right combination of skills, you could increase or decrease the amount of speed you gain based on the strength of the ritual and the time spent powering up. You could also have the power available as a quick and dirty evocation tied to a danger sense time enchantment, allowing you to power up in unexpected situations, but with the drawbacks of the internalized power source (life force powered) or local temporal disturbances. The winding the spring/stretching the rubber band ritual treads very close to breaking the Law, however.
