You may cast sorcery spells as though they had flash. (You may cast them any time you could cast an instant.)
11/17/2017 Hypersonic Dragon’s last ability applies to sorcery cards in any zone, provided something is allowing you to cast them. For example, you could cast a sorcery with flashback as though it had flash.
11/17/2017 Hypersonic Dragon’s last ability has no effect on abilities that you can activate “any time you could cast a sorcery.”