sumtime.awk

#!/usr/bin/awk
# sumtime.awk: sums up times
#   input: lines with time indications of the form hh:mm, e.g. 12:30 or 4:15
#   output: the sum of the times, e.g. 16:45

/[0-9]{1,}:[0-9]{1,2}/ {
    split($0, fields, ":")
    hours += fields[1]
    minutes += fields[2]
}

END {
    hours += minutes / 60
    minutes = minutes % 60
    printf("%d:%02d", hours, minutes)
}