I'm looking for the weather forecast and it says that in Nikko there will be snow on the 2nd and the 3rd.The temperatures are forecast to drop considerably on the 3rd, but the risk of snow in the town of Nikko is very low. There is some rain predicted for the 2nd, though. In the higher elevations of Okunikko, there is a chance of snow during the night, but it would likely be rained away or melt during the day when temperatures are unlikely to remain below freezing.
I don't know if it is better to change the day, maybe the 4th ore the 5th..
Weather forecasts are not very accurate over a time period of more than 2-3 days. If you can remain flexible, it would be ideal to decide just one day in advance when forecasts are usually very accurate.