Three days is enough. It is just the time when the ice and snow festival is on. So go skiing and seeing the ice sculptures are definitely a must. Go Yabulin International Ski Resort for skiing and see ice scuptures in Harbin Ice and Snow World, Ice Lantern Garden, Sun Island Scenic Area and Zhaolin Park. If there is still time left, go to Central Street (Zhongyangdajie) and St.Sophia Church.
Wish you a nice journey!