I'm working on an Excel 2010 spreadsheet and I'm trying to put in durations for some tasks I want to schedule.

The interesting thing is that up until a few minutes ago, I couldn't do it.

I was entering in "47:00" and excel was (and still is) converting it to "1/1/1900 23:00:00"

In my mind, I want the value to be 47 minutes, but for the life of me I cannot find a fix for this behavior.

Here's the weirdest thing, I haven't had this problem in the past.  Usually I put in times, add them up and they work like magic.  Put in 18 entries of 20 minutes each, total them and excel will usually tell me that it's a total of 6 hours.

No problem.

Today, problem.

Here's the weird bit:
As I was writing this post, I got it to work.
By formatting the column as custom "[hh]:mm" and summing the columns, I can get total times.
But the times are still being formatted into dates if I look at the underlying data. 

Bottom line, if you need to calculate durations, you can, but don't look too closely at what is happening underneath the covers.