If that cookie comes from CEF then use the CefBaseTimeToDateTime function available in the uCEFMiscFunctions unit of the CEF4Delphi project to convert it.

TCefBaseTime is an int64 that represents a wall clock time in UTC.

Values are not guaranteed to be monotonically non-decreasing and are subject to large amounts of skew. Time is stored internally as microseconds since the Windows epoch (1601).