The explanation of the 3rd index of the tuple returned from _winreg.QueryInfoKey(key) explains that it is a long representing 100s of nanoseconds since 1/1/1600.

However, when I use this value and convert to the actual date using 
startDate = datetime(1600,1,1)
lastModified = QueryInfoKey(key)[2]
print "%s" % startDate + timedelta(seconds=lastModified*(10**-9)*100) 

The date is about right except for the year value, it's off by one.

I suspect the documentation should say the value in the tuple is the time since 1/1/1601 instead of 1/1/1600. This would corroborate Microsoft's documentation that makes references to 1/1/1601 (i.e. http://technet.microsoft.com/en-ca/aa393040(v=vs.90).aspx)