Add 1% Calcium Chloride and it is equivelant of raising your setting temperature 10 degrees. 2% would make 50 degree weather set up concrete like 70 degree weather (much quicker). (Sugar will do the opposite for very hot days where you want to delay the concrete from setting up). You used to be able to get Calcium Chloride from Lowe's..... it was sold as ice remover for roads and driveways.......

Or just let them dry an extra day or two......