Cellaring period is years from vintage. This is considered a maximum period for continued development e.g. 2006 Marsanne will develop added character & complexity for another 7 to 10 years from its vintage year i.e. until 2013 to 2016.
By the same token many wines (whites and reds) will hold their development and continue to be superb drinking beyond this arbitrary period.
When to drink it or when it is at its "best" is a subjective judgement based upon individual palate preference.