Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Osaka to Harbin as you normally would.
In terms of precipitation, rainfall in Harbin ranges from 0.0 - 5.9 inches per month. July is typically the wettest month, when rainfall can reach 5.9 in. January is typically the driest time to visit Harbin when rainfall is around 0.0 in.
If weather is an important factor for your trip to Harbin, use this chart to help with planning. For those seeking warmer temperatures, July is the ideal time of year to visit, when temperatures reach an average of 71.6 F. Travelers looking to avoid the cold should look outside of February, when temperatures are typically at their lowest (around 6.8 F).