These are sold by the pair. They are fairly quick drying, but it greatly depends on conditions, i.e. humidity, wind, etc.
These are sold as one pair. Concerning drying time, it will depend on the humidity and wind as much as temperature. In most regions, nighttime humidity is higher than daytime. I recommend drying them during the day, in the sun and wind if available. I also recommend ordering at least one size larger, as these socks are very narrow. They are well made, and hold up pretty well in the wash.