On my rMBP, there's a greyed-out "Collecting power usage information..." in the battery menu-bar pull-down.
Perhaps this means that time estimations will come after a period of observation. If so, that would be smart, as time-remaining depends rather heavily on the software you use, its CPU demands, and its utilization of the power-saving technologies integrated into Mavericks (such as Timer Coalescing and App Nap).
If I'm correct, then after a week or two you may have timing information available that is based on your actual usage, and that should be more accurate than ever.
It's something to hope for, at least...