I must have done something wrong, but I can't figure out what it is. Here is what I did and an example of the results.
I created two formulas (one called Difference, and one called TotalTimes)The first one holds the first formula that you posted, and the second refererences the first but adds a runnig total for the group.
When ther is only one song (total is less than 10 minutes), it works fine.
Assorted Ozzy
Shot In The Dark 4:16
Total Time 4:16
The problem comes when the total is greater than 10
Assorted Marshall Tucker
Heard it In a Love Song 4:57
Ramblin' 5:07
Running Like the Wind 9:10
Fly Like An Eagle 3:02
This Ol Cowboy 6:47
Losing You 5:09
Long Hard Ride 3:51
Searchin For a Rainbow 3:32
Total Time 17:35
I don't know where the mistake could be I double and triple checked the formulas.
This is the formula for Difference:
DateDiff("s",DateTime(CurrentDate,Time(0,0,0)),DateTime(CurrentDate,Time({Tracks.TrackLength})))
This is the formula for TotalTime:
Time(DateAdd("s",Sum({@Difference},{Recording_with_Album_Covers.RecordingID}),DateTime(CurrentDate,Time(0,0,0)))).