Best time to visit Switzerland is between April and June even September and October are good months to visit but it will be cold enough . temperature wil be around 12-15 degrees and in high altitude areas it will be more chilled around 4-5 degree.
Switzerland is all about nature. The same place looks different in different seasons. My personal favorites are Spring and Autumn. Especially Autumn till first week of November will be magical to see in the valleys.But winter is already started on the mountain tops. So in both Spring & Autumn - you can enjoy lot of Snow + Greenery with a compromise of day time.
From last Sunday of October the Day Light Savings will be switched off which results in one hour early sunset. Also the day time will be reducing until December 21.