I import data representing telephone call duration from a csv file
ie
001:00:12
013:15:59
124:42:13
and want to sum it using SUM(A1:A3)

If I copy from the csv file and paste into Excel the format of the text data remains untouched even if I have previously formatted cells A1>A3 as [h]:mm:ss

If I manually overtype the cells ie in A1 (eg type 1:0:12, and 13:15:59 and 124:42:13) the cells display correctly (except no leading zeros) and the formula then starts to calculate correctly . In effect I am retyping every cell value so that the formula calculates correctly. Any help very much appreciated.