I'll guess at that one. The receiver determines position based on the differences in delay of the signal from each satellite. Since the signal from each satellite will be delayed by the same amount by the antenna lead, that delay will automatically be cancelled out of the calculation. So the GPS will accurately return the position of the antenna.
As for time, the GPS will use the calculated position to determine the time delay from each satellite. Since the calculated position is at the antenna, it will only account for the over-air delay, not the delay in the antenna lead. Since the signals actually take longer to reach the GPS than is accounted for in the calculation, the reported time will be sightly slow (i.e. earlier than the actual time). By something like 30 to 50 microseconds, if my math, Latin prefixes, and assumptions about the speed of the signals in the lead are correct.