When you need to sum up all the value of minutes and seconds, you will need to convert the string format into number then you can start the calculation, however I am unable to provide a single step solution but would need some helper column to do so:
Multiple steps
First, from the "AHT" column you already created, I will obtain the minutes portion by creating a new column:
minutes = VALUE(LEFT(Sheet1[Time],2))
Next, I will create a new column to store the seconds also:
seconds = VALUE(RIGHT(Sheet1[Time],2))
Finally, I will create a new measure to sum the duration of minutes and seconds with the following formula:
duration =
var sec = MOD(SUM(Sheet1[seconds]),60)
var minute = TRUNC(DIVIDE(SUM(Sheet1[seconds]),60)) + SUM(Sheet1[minutes])
return
FORMAT(minute,"General Number") & "minutes " & FORMAT(sec,"General Number") & "secs"
Here is my original table with two new columns:

By setting the calculated measure as field, I will get the following scorecard, you may choose other format like "00:00" if you prefer :)

Single step to return the same result using dax formula with measure:
Duration =
var minutes = SUMX(Sheet1,VALUE(LEFT(Sheet1[Time],2))) + SUMX(Sheet1,TRUNC(DIVIDE(Sheet1[Time],60)))
var seconds = MOD(SUMX(Sheet1,VALUE(RIGHT(Sheet1[Time],2))),60)
return
FORMAT(minutes,"General Number") & " minutes " & seconds & " seconds"