lowstring,
You never stated the Format or the Datatype of this "Duration"
If it is real "Time" DataType, and formatted like this (hh:nn:ss):
0:03:15
0:12:30
0:00:04
... or formated like this: (hhh:nn:ss):
00:53:15
00:12:30
00:00:04
Then you can simply use this as the ControlSource of a TextBox in your Report Footer:
=Sum([TimeDuration])
Then set the format of the textbox to:
hh:nn:ss