What's the time dilation of a rocket moving at light speed?

Actually, you experience time slower near the speed of light.

At speed of light time might be at a stand still or reverse (hypothesized by physicists but unable to be proven) but such a question is pointless since matter cannot go as fast as light (ever).

The dilation would depend on how "just below" light speed it really is.  The closer it is the more dilated time is.

The persons who are actually on the rocket will experience time in the same manner as persons who are at rest, e.g. on Earth.  To an observer at rest, however, the persons in the rocket would appear to be moving slower and time would appear to be passing more slowly.  In theory, if you could accelerate a rocket up to a speed that is near the speed of light (we can't do so with present technology) and send it out into space for a long period of time (e.g. 40 years), when it returned, everyone on Earth would have aged 40 years but the persons on the rocket would have aged much less because time (relative to time on Earth) will have slowed down for them.