The time of year that's best to plant butternut squash in your area will depend on the weather.
Butternut squash should be planted only when all dangers of frost are gone and the soil should also be warmed enough by the sun to at least 60 F.
If there's any danger of frost in the forecast then you should not plant the squash outdoors yet.
So if you have frost during spring then you should start the plants of butternut squash indoors and then only plant them after all frost is gone for the season so you may have to wait until around April or May before planting the butternut squash to avoid it freezing.