You can but there's always some risk involved in travelling to north Sikkim till February because of snowfall which blocks roads and also sometimes landslides.
February would be extremely cold. I went there in april and it was still freezing cold. plus the roads are not in a very good condition. if you can bare the cold..you may try, else april may are ideal months.
If you are a fan of snow, then winter months are the best time for you to visit Lachung. Usually starting from October and continuing till February, the winter breeze brings heavy snowfall which makes the whole region milky white. Some of the most amazing sightseeing options open during the winters in Lachung.