if you have duration in format of 3h55m2s in a file, this snippet can calculate the cumulative time duration

compute-total-duration.go

package main

import (
	"bufio"
	"log"
	"os"
	"time"
)

const fileName = "test.txt"

func main() {
	fil, err := os.Open(fileName)
	if err != nil {
		log.Fatal(err)
	}
	scanner := bufio.NewScanner(fil)
	var totalTime time.Duration
	for scanner.Scan() {
		duration, err := time.ParseDuration(scanner.Text())
		if err != nil {
			log.Fatal(err)
		}
		totalTime = totalTime + duration
	}
	println(totalTime.String())
}

test.txt

19m10s
8m43s
16m34s
13m10s
16m48s
7m34s
9m22s
20m18s
5m39s
16m01s
8m42s
4m13s
18m45s
13m56s
9m34s
9m32s
19m52s
7m27s
9m41s
8m12s
5m31s
12m59s
13m41s
5m46s
5m57s
5m24s
1m17s
8m48s
21m45s
15m50s
7m07s
17m01s
4m37s
10m28s
5m55s
6m02s
4m52s
9m31s
4m24s
3m41s
13m56s
18m02s
5m26s
13m43s
2m30s
4m27s
3m57s
6m49s
3m29s
6m09s
2m57s
6m17s