Parse XML, date formats (PT0H0M0S,PT2920H0M0S)

I'm trying to parse an xml-file exported from MS Project 2013 using python and it contains the following data:

<TimephasedData>
    <Type>1</Type>
    <UID>4628</UID>
    <Start>2014-09-22T08:00:00</Start>
    <Finish>2015-09-22T08:00:00</Finish>
    <Unit>8</Unit>
    <Value>PT2920H0M0S</Value>
</TimephasedData>
<TimephasedData>
    <Type>1</Type>
    <UID>4628</UID>
    <Start>2015-09-22T08:00:00</Start>
    <Finish>2015-09-23T08:00:00</Finish>
    <Unit>2</Unit>
    <Value>PT8H0M0S</Value>
</TimephasedData>

What I don't understand is what the PT8H0M0S and PT2920H0M0S represents (TimephasedData). Currently I parse the dates by replacing the character "T" and then use strptime