Like all digital currencies, Dash is traded on crypto exchanges 24 hours a day, 7 days a week. The exchanges define the price based on supply and demand, i.e. based on the interest from buyers and sellers. If there are more people willing to buy than sell, the price will rise.
That said, supply and demand is strongly dependent on other factors, such as increasing global adoption of digital currencies, the broader crypto markets, and technological advancements.