As no-one knows what route the McCanns would have taken between the apartment and the Millenium Restaurant it would seem to be pretty much a pointless question unless someone can enlighten us about that matter.
There are two very practical routes.
The first is the shortest (about 520m / half a kilometre, or 580 yards / one third of a mile.) It goes north from the apartment along roads which would not probably have been familiar to the McCanns.
The second is slightly longer (about 700m/ seven tenths of a kilometre or 770 yards / 0.44 of a mile). This, I would suggest is possibly a more likely route as the McCanns would already know half of it as it passes the main reception where they would have picked up their keys and the kids clubs where the children went each day.
This latter distance also tallies very closely with the claim that Kate McCann made that the Millenium was nearly half a mile from their base (the apartment block).