Using formulas with pivot table sums

[dogburster]

Hello, I have set up a pivot table to summarise some report data and need to apply a 30% or 70% calculation to some of the times (format [hh]:mm:ss to create a new table of data, what would be the best way to do this? Is it possible to do it within the pivot table by referencing a matrix on another tab which has criteria that Vlookup could use to determine what calculation to apply? I'm unable to post images, Pivot and matrix are structured identically:

Codes Codes Codes Codes
Store numbers
Store numbers
Store numbers
Store numbers


Pivot table has times as values, matrix has 3 different options, two of which require a calculation of either 30% or 70%

Thanks