Midnight Mystery is one of my favorite 'older' daylilies. It is much darker than the photographs suggest an has an etherial glow when it is backlit in the morning. In my zone 5b garden it does very well with little care. Blooms reliably and sends up new fans every year. It went from 2 fans to a sizable clump in 3 seasons. It does occasionally send a fan out some distance from the grown so keep that in mind if you're planting it among other daylilies.
It is an early mid season bloomer. That is to say, it's not among the first group to bloom but it's the first among the mid season bloomers. For me I see scapes in the range of 30-34 inches with 3-4 way branching and bud counts on target around 20. Does not rebloom for me rather it tends towards summer dormancy. It doesn't go completely dormant but there is definitely a rest period before it starts growing again.