Converting unusual time format

I'm trying to calculate the downtime of some network kit using it's factory tools, but the exported report format for the time period is shown as (for example) "4d 15h 10m" for 4 days, 15 hours and 10 minutes.

Is it possible to convert this format to either hh:mm or dd:hh:mm, so that I can calculate the SUM totals?

Alternatively, if it helps, it also shows the start and end date/time of these periods in the following format:
"Wednesday, September 12, 2012 18:53:17" so it might be possible to work out new downtime periods and use them instead.

Many thanks in advance,
Dave.