Depends 100% on what is Facilitating this chronological alteration
As mentioned by another, a possible facilitation of this is a sort of "time-envelope" that envelopes the object within a set amount of space for a set amount of time (I'm assuming the effects are temporary) set by the caster. - Objects within envelope experience time to be the same relative to each other. - The surface of the envelope is the boundary of chronological field, may be a sharp boundary (perhaps even visible as it would affect light passing through as though slightly refractive) or a more fuzzy boundary where there's a bit of transition between time speeds. - What happens though if half an object is in this field and the other half is outside? Or does the whole object have to be contained to work? Can I age just my scalp faster than the rest of me to grow hair quickly, fingertips for nails? - Objects close to the effected object would be slightly affected the closer they came to the object until entering the envelope and being brought up/down to speed. The collision itself wouldn't seem to be impacted by the change in time flow itself, simply occurring sooner/later than normal. (unless part of the collision is to create a new time-envelope on what ever was hit)
Object specific time alteration, where it is not the space taken up by the object, but the object itself that is altered on the time line. - The matter of the object itself is targeted and the interaction of time with that specific matter are effected. - Effective changes to time would be visible through other observable phenomenon. Doubling in velocity, squaring of effective mass/inertia, a slight squeezing/stretching of the object to external observations, to whatever ratio matching the change in time speed. - A one off effect, rather than a persistent field. (Increase/decrease existing qualities to compensate which then becomes its new "normal time" qualities) - Affect on non-altered objects would be the same as if affected by a normal object with the new qualities (Hits twice/half as hard etc)
Magic - (You basically just write the rules) Time is a magical force that can be manipulated much like heat, light, and physical work. 781
- Magic can place the affected in a demi-plane bubble with different properties than the normal universe. - A magical force pushes or pulls against the stream of time like a paddle, pushing your time bubble further up or down stream. - A time bubble, when colliding with an object of normal time may POP, causing chrono-side effects (potentially wanted effects in the case of arrows etc) or the bubble may remain in tact and cause the object to "bounce" off. Such a bounce may inadvertently Push the normal-time object forward in time slightly. Pushed hard enough, you might send something or someone into next week!
But again, it just depends on how the whole time altering even works. With more details, I'm sure I can give better options.
General Sanity comments: - A fraction of a second's worth of "absolute position" in a constantly moving universe would be detrimental to any to discover it, instantly slamming you into the earth, space, or nearby structures. - Gravity is not apart from Time, as gravity is shown to affect the passage of time, so an object frozen in time would not likely suspend itself midair as the non-time stopped earth would still have it's full pull on it (or the envelope of time containing it). - There's all sorts of fun to be had with the boundary of a time bubble. Imagine a troop of archers lined up for a volley. A bubble is placed around them to make them fast compared to outside. Suddenly that single volley becomes a carpet of every arrow in their quivers as each shot slows at the boundary while they load and shoot the next volley. - For interactions between time affected and non-effected objects, I would generally treat the acceleration of time as a multiplication of energy, and a slowing of time a division of energy, until time became normalized relative to the two again. 781