Ther last time the Beltline didn't have a tower crane somewhere would have been around 2004. After Emerald Stone was completed there might have been a gap before Chocolate started construction. If not it would have been about 2002.
If all goes reasonably well without any major hiccups, it'll be ready for occupancy October-November 2020. Given how the building isn't anything too out of the ordinary, it should be okay for that timeline.