Calculate Time in bash

#!/bin/sh
# +0:00 or +00:00 or -0:00 or -00:00
# returns seconds as int
function getSeconds() {
 SIGN=$(echo $1|cut -c1)"1"
 HOUR=$(echo $1|cut -d':' -f1|cut -c2- )
 HOUR=$(echo "${HOUR#0}")
 MIN=$(echo $1|cut -d':' -f2)
 MIN=$(echo "${MIN#0}")
 SECONDS=$(((HOUR * 3600) + (MIN * 60)))
 echo $((SECONDS * SIGN))
}

# seconds as int -10, 0 or 70
# returns +0:00 or +23:00 or -1:00 or -11:00
function formatSecondsToTime() {
 dt=$1
 SIGN="+"
 if [[ $1 -lt 0 ]] ; then
  SIGN=$(echo $1|cut -c1)
  dt=$(echo $1|cut -c2-)
 fi
 dm=$(((dt / 60  ) % 60))
 dh=$(((dt / 3600) % 24))
 VALUE=$(printf '%d:%02d' $dh $dm)
 echo $SIGN$VALUE
}

function addMinutes(){
 SEC1=$(getSeconds $1)
 SEC2=$(getSeconds $2)
 CALC=$((SEC1 + SEC2 ))
 #echo "$1 $2 $SEC1 + $SEC2 = $CALC formatted= $(formatSecondsToTime $CALC)"
 echo $(formatSecondsToTime $CALC)
}

function printTime() {
 SECONDS=$(getSeconds $1)
 echo "$1 $SECONDS $(formatSecondsToTime $SECONDS)"
 #echo "$1 $SECONDS $(formatSecondsToTime $SECONDS) $(getSign $1) $(getHours $1) $(getMinutes $1)"
}

# test
printTime "+00:01"
printTime "-00:10"
printTime "+01:00"
printTime "+09:10"
printTime "+09:01"
printTime "-11:10"
printTime "-09:59"
printTime "-23:59"
printTime "-10:59"
printTime "-000:059"
printTime "-25:89"
printTime "-24:61"
printTime "-24:00"

Output:

+00:01 60 +0:01
-00:10 -600 -0:10
+01:00 3600 +1:00
+09:10 33000 +9:10
+09:01 32460 +9:01
-11:10 -40200 -11:10
-09:59 -35940 -9:59
-23:59 -86340 -23:59
-10:59 -39540 -10:59
-000:059 -3540 -0:59
-25:89 -95340 -2:29
-24:61 -90060 -1:01
-24:00 -86400 -0:00

time="+01:22"
echo $(addMinutes $time "+0:01")
echo $(addMinutes $time "-0:01")
echo $(addMinutes $time "+1:01")
echo $(addMinutes $time "-1:01")
echo $(addMinutes $time "+24:01")
echo $(addMinutes $time "-24:01")

Output:

+1:23
+1:21
+2:23
+0:21
+1:23
-22:39