adding imported time segments, mainly in seconds. ( :ss)

Daily, I import a long column of data broken down in time (minutes and seconds) up to 150 rows.
I need to get a sum of the entire column. The numbers, minutes and seconds, appear randomly in the rows. example;
:55
:33
:48
1:48
:31
:03
12:34

The sum should be 17:12 (mm:ss)

Because of the random mixed formatting ( :ss & mm:ss) I can't seem to find a cell formatting that works well for adding these.
The final result, I want to display in the format h:mm:ss
(often totals are around 18 hrs, 25 min, 32 sec - 18:25:32)

Any help would be greatly appreciated.