Yes, like two days when you have Form 15.25. Or you may get Form 15.30 which gives you a longer time if you meet certain conditions.
Both forms must be acquired at the very first border crossing, otherwise you will do a tax and/or duty violation. If caught you will be liable for any tax and duty due PLUS up to 5 times the tax and duty as penalty.
Art. 118 Swiss Customs Law. http://www.admin.ch/opc/de/classifie...ndex.html#a118
Considering tax for a car is 4% + 8% = 12.32%, you may have to pay up to a total of 73.92% of the cars value (and more if duty is due)
Edit: Additionally up to one year in jail or a fine up to CHF 30'000 http://www.admin.ch/opc/de/classifie...index.html#a14