#!/bin/bash

list="1:51:59 0:33:08 2:06:41"

h=0
m=0
s=0
for x in ${list}
do
        echo ${x}
	S=${x##*:}	# Extract seconds.
	x=${x%:$S}	# Strip seconds from x.
	S=${S#0}	# Strip leading 0 from S.

	M=${x##*:}	# Extract minutes.
	M=${M#0}	# Strip leading 0 from M.

	H=${x%:*}	# Extract hours (assume there is no leading 0 here.

        h=$(( h + H ))
        m=$(( m + M ))
        s=$(( s + S ))
        #echo "H : ${h}"
        #echo "M : ${m}"
        #echo "S : ${s}"
done

m=$(( m + (s/60) ))
h=$(( h + (m/60) ))
m=$(( m % 60 ))
s=$(( s % 60 ))

echo "${h}hrs ${m}min ${s}sec"

1:51:59
0:33:08
2:06:41
4hrs 31min 48sec

1:51:59
0:33:08
script_name: line 14: s + 08: value too great for base (error token is "08")
2hrs 24min 59sec