The exact answer to this would depend on a couple of things, I'll try and explain this point by point:
A) Does it hit immediately?:
A seeking weapon will not hit the target immediately it is launched in the same hex, as it would have to enter the hex of its target while in flight (i.e. move into the target's hex or have the target move into its hex after it has been launched).
B) Does it hit next sub-pulse?
It could do, yes. The next sub-pulse will be sub-pulse 1 of an impulse. On this sub-pulse, only things moving at speed 24+1 will move. So, if the target is at this speed, he moves once before any drones would move, and would then move again on the second sub-pulse, whereupon the drone would also move. Note that in this case the target is ahead of the drone and will stay there if he keeps going straight away from the drone at speed 24 or 24+1.
If the target is moving at less than 24+1, neither the target or the drone will move on the first sub-pulse. If the target is moving at speed 24, speed 16+1, speed 16 or speed 8+1, it will move on the second sub-pulse, and will be one hex from the drone. At this point, the drone could (and must if it means it would score a hit by doing so) make a high energy turn (4F3e) and then move into the target's hes, scoring a hit.
If the target is moving at speed 8, it will not move on sub-pulse 2 but the drone will. At this point, the drone will hit the target either by moving straight ahead, or by making a high energy turn if this is necessary (it cannot sideslip as it has not yet fulfilled its sideslip mode, not that this matters here).
However, if the seeking weapon is a plasma torpedo, it would simply be able to make a HET on the first sub-pulse of the impulse after lanch (because it moves at speed 32) immediately after the target has moved, thus hitting on the first sub-pulse.
C) Will the seekign weapon overshoot?
If the seeking weapon launched is a suicide shuttle, it is possible that it will overshoot as it must move forwards on its first move because it will not yet have fulfilled its turn or sideslip modes (both 1) and cannot make high energy turns (4F3e). So, unless moving straight ahead would place it in the same hex as the target, it would not hit with its first move. After this, it could turn or sideslip to try and hit the target.
Does that help you? Also correct me if I myself have messed up the rules somewhere.
