In New York, The dates for pension valuation are from the date of marriage until the date the divorce action is commenced. If there was a period of time before the commencement of the divorce action where the parties were separated, such a period of time will not impact the martial portion of the pension.
The marital portion of the variable supplement (457 etc) is also marital property. Like the pension, the variable supplement is measured from the date of the marriage to the date of commencement. Any gains or losses are also factored in until the date of distribution.