Need to display hours and minutes within a TAT formula

The reason you are getting 0 for the one hour duration between the two date/time fields is the formula converts both date/times to days.  Assuming both are on the same date, the conversion to date results in 0 days difference between the two.  Also, using Days at the beginning of the formula will return days (not hours).

What is the data type of your formula field?  Can you share a screenshot?  

Could you just subtract rec'd from ack?

[Acknowledgment Date/Time] - [Communication Received Date/Time]

Here is the screen shot of the field...sorry for the delay got pulled into a bunch of stuff!  If you have a suggestion would love to hear it!

hueyal is right about the 0. ToDate drops the time, so anything received and acknowledged on the same day comes out as 0 days.

Make the field a Formula - Duration and subtract the date/times directly. That keeps the hours and minutes:

[Acknowledgment Date/Time] - [Communication Received Date/Time]

If you still want to skip weekends like WeekdaySub was doing, take the weekend days back out:

([Acknowledgment Date/Time] - [Communication Received Date/Time]) - Days(ToDays(ToDate([Acknowledgment Date/Time]) - ToDate([Communication Received Date/Time])) - WeekdaySub(ToDate([Acknowledgment Date/Time]), ToDate([Communication Received Date/Time])))

Set the display to HH:MM. Something received Friday at 4 PM and acknowledged Monday at 9 AM comes out as 17:00 instead of 65:00.

It assumes communications come in on weekdays. One received on a Saturday or Sunday will be a little off.