Hi,
I assume that you import a textfile. In case yes, assign the : sign as delimiter. Now you get two columns. The first column (A) with minutes you just make a sum of. The second column (B) with seconds you make a sum of and divide the result by 60. After this you just summarize the two sums (A+B) and divide the result by (60*24) to get the result in days. This you format as hh:mm:ss. If the total is more than 24 hours you have to handle this by special formulas.

Kind regards
Bjorn