All 'time values' in C are texts. Convert them to real time values first. Select column C. Then on the Data ribbon select Text-to-columns and press Finish without changing anything.
Now the formulas in D will work, though I wonder why you want to present the outcome within a TEXT formula. Much easier to just use the SUM, SUMIF and SUMIFS and specify a custom format as [h]:mm:ss
The square brackets surrounding the h will allow you to keep summing in case the sum would ever exceed 24 hours.
See attached file.