I hesitate anymore to recommend specific practices for specific days of the calendar, as everyone is on a different path and it's all Qigong anyway. My personal practice is grounded in Wujigong so I am inclined to the Heaven-Earth Qigong form or the Hunyuan Twelve along with extended Wuji meditation on Solstice and Equinox days. But again, the rationale and purpose behind it is the same with all Qigong practices, to connect with the Dao; to acknowledge the Taiji of the Universe and the Wuji that underlies it all.
In the final analysis it's all made up anyway: time, Qigong, meditation, all of it. But we exist within this flux of energy that has discernible patterns and similar repeating experiences. So we recognize it, name it, play with it, use it to direct our attention back to that which is before flux, beyond form and pattern. In the end that is the Human experience anyway. We might as well experience it at as high a level as possible.