JIRA uses the '3h 15m' style notation which works for me.
Oh the other hand, I used a timesheet system in which time was entered in 15 minute blocks. I found having to enter times as a decimal values like 3.25 was non-intutive way of expressing a duration of 3h 15m.
On the example given, couple of things are not clear:
What is the granularity? Minutes?, 5 minutes or 30 minutes? If showing something like 24 hour days split into several states, I would be thinking along the lines of percentages or segmented bar graphs rather than hours/minutes which might be too precise for a view. Also remember that twice a year you get 23 or 25 hours.
Finally, pet peeve as a non-american; that day format just looks wrong to me. I get your users might be only US based, but I would still lean towards something like Mar-18, Mar-19 or have a header cell with March and sub-headers with 18 | 19 | 20.
