ok, think I've figured out how to split the values using a combination of LEFT, SUBSTRING and CHARINDEX.
The result is something like this:
,CASE WHEN [calendar_duration] LIKE '%Day%' THEN LEFT(SUBSTRING([calendar_duration],CHARINDEX(' Day', [calendar_duration]) -2, 2),CHARINDEX(' Day', [calendar_duration]) - 1) ELSE '00' END AS [Days]
,CASE WHEN [calendar_duration] LIKE '%Hour%' THEN LEFT(SUBSTRING([calendar_duration],CHARINDEX(' Hour', [calendar_duration]) -2, 2),CHARINDEX(' Hour', [calendar_duration]) - 1) ELSE '00' END AS [Hours]
,CASE WHEN [calendar_duration] LIKE '%Minute%' THEN LEFT(SUBSTRING([calendar_duration],CHARINDEX(' Minute', [calendar_duration]) -2, 2),CHARINDEX(' Minute', [calendar_duration]) - 1) ELSE '00' END AS [Minutes]
,CASE WHEN [calendar_duration] LIKE '%Second' THEN LEFT(SUBSTRING([calendar_duration],CHARINDEX(' ', [calendar_duration]) -2, 2),CHARINDEX(' Seconds', [calendar_duration]) - 1) ELSE '00' END AS [Seconds]
Converting each value into seconds then summing everything up should be much easier :-)
I'm sure there are more efficient ways to do this but it won't be in frequent use so it'll do for now.