The book records the twelfth day of the second lunar month, so the Gregorian calendar should be February, March and March. The possible constellations during this period are Aquarius, Pisces and Aries. According to Daiyu's delicate beauty and crying characteristics (especially this one), she can't be an impulsive and brave Aries, let alone an unreasonable water bottle. Choosing Pisces is easy-end of reasoning.
I also like a dream of red mansions and constellation research.