Timestamp diff in Hours

[adoremars]

Hi,

I have a open date (May 15, 2007 9:21:25 AM) in this format.
And a close date (May 18, 2007 10:05:42 AM) in this format.

I need the difference in hours. ie if the diff is 45 minutes i need it in 0.45 format
and if the diff is 1 hour 45 minutes i need it in 1.45 format.

Can anyone help me to achieve this?

Thanks