No problem, now it's clear. Let's try again. How about:
The call to Interval() will make sure that very big values will still be converted to a massive amount of hours...For example, this application of the same expression on the last value in your Excel file:
If you want different formatting, check Andrews post which contains a lot of useful advice.
[Edit] Sorry for the spam, post contained a lot of grammar and spelling mistakes. Time to go home