Excel doesnt really have a duration data format. It has time and a difference in time can be done using subtraction. the difference can be viewed in the format you are showing above "00:41:00" but if you view the custom format dialog in excel, you will see it is the same as 12:41:00 AM.
Meaning it is just a time past midnight formatted to show 12 am as 00.
So... that being said, once we understand how excel stores duration as time, i am thinking that we can just write Ians final formula in one cell, no extra columns needed.
=DURATION(,,HOUR(B2),MINUTE(B2),SECOND(B2))
(Yes i just did this to verify, sent from excel to my ipad and added the formula, worked perfectly, confirming that the number being brought over from excel is just a Time format)
Jason