Well, since I worked on it I'll paste what I've now got on my clipboard. AFAIK, you'd need an integer field and a calculation that you perform on a form or query. If TimeSum contained 359 (5 min. 59 sec. in your example) then this would return 06:59. I see that the value is rounding up, which is no good, but since you already have an answer I'll leave it at that for now.
Code:
SELECT tblTimeSums.TimeSum, Format([TimeSum]/60,"00") & ":" & [TimeSum] Mod 60 AS TimeCalc, Format([timesum]/60,"00") AS expr1
FROM tblTimeSums;
EDIT
Changed my mind. So this works if you don't need leading zeros in the minutes portion. Otherwise, wrap the Int function in the Format function I guess
Int([TimeSum]/60) & ":" & Format([TimeSum] Mod 60,"00")
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.