Subtracting time values within a string in xsl

Hey, I am trying to subtract an initial time value from consecutive time values using xsl in order to produce a delta value. The problem is that the way the program creating the files stores the data, it also has the date, etc. as a string. Any ideas on how I can accomplish this? An example of the xml code is below:

<Data>

<P>

<Name>Extra 1</Name>

<Time>Jun 14, 2007 3:28:12 PM</Time>

<Value>24.461850550949727</Value>

</P>

<P>

<Name>Extra 1</Name>

<Time>Jun 14, 2007 3:28:13 PM</Time>

<Value>20.30450417966249</Value>

</P>

So basically I want to be able to subtract the second time value from the first (and I'll later be adding milliseconds)

[776 byte] By [paulnc8a] at [2007-11-27 10:16:59]