The festival runs from roughly mid-December to late February, and the opening ceremony is fixed to 5 January. But Ice and Snow World's actual open and close dates move every year with the ice — the site is built from the river and it comes down when it stops being safe. Confirm the current season's window before you contract departures rather than after.
−25 °C to −30 °C is normal during the festival. Every day plan we run here is built around hourly indoor stops with hot drinks, and a group without proper cold-weather kit will cut the day short regardless of what the itinerary says. This is the single most common reason a Harbin day underdelivers, and it is entirely preventable at the briefing stage.
There are three defensible answers and they suit different groups. Before 16:00 gets you the ice unlit and then the lights coming up, which is the fullest version. Arrival afternoon front-loads the trip's biggest thing onto day one. A pure night visit is the shortest and coldest. We publish the first as the default; say which you want and the day is built around it.
Harbin itself has four and five-star stock. Snow Town and Snow Valley do not — accommodation there is village guesthouse standard on heated brick kang beds, often with shared bathrooms. That is the character of those places rather than a failure of them, but a guest who booked on the strength of a Harbin hotel photograph needs telling before departure, not on arrival.
HRB takes direct flights from Beijing, Shanghai and several regional hubs, which makes a three-night Harbin block the easiest winter module to bolt onto an existing routing. Going the other way, high-speed rail reaches Changchun in about an hour and opens the Jilin side — Puyi's puppet palace, then Changbaishan's ski slopes, flying home from the mountain rather than doubling back.