60 minutes is 1 hour, so all you need to do is increment the hour by one. This can be done by adding 100
to the HHMM
time as shown below:
start="$1"
# add 100 to the start time to increment the hour
newTime=$((10#$start+100))
# check if we have crossed midnight
if (( newTime >= 2400 )); then
newTime=$((newTime-2400))
fi
#pad with leading zero
newTime="$(printf %04d $newTime)"
echo "$newTime"