from 7pm to 9pm the tree lighting ceremony will take place at Rockefeller Center. avoid 5th Ave in the 50's. I wouldn't be surprised if 6th Avenue also has congestion.
all buses in the area are also being rerouted which may cause additional congestion, so perhaps it may be better to avoid the whole thing?
Perhaps you will get more passengers hailing in Times Square if that isn't too congested? If that's bad get out and go west, 51st Street tends to run well west from 7th Avenue.