Update, compare kernel versions - reboot within 6hours period - CentOS

#!/bin/sh
host=`hostname -f`
date=`date`

# run updates to get latest software and kernel
yum -y update
maxdelay=$((6*60))
rdelay=$(($RANDOM%maxdelay))
sdelay=$(($rdelay*60))
kernel=`uname -r`
latest=`rpm -q kernel --queryformat '%{installtime} %{version}-%{release}.%{arch}\n' | sort -n -k1 | tail -1 | cut -d ' ' -f 2`
sdate=`date`

if [ "$kernel" = "$latest" ];
then
        echo "No need to reboot..."
        echo "You are running the latest kernel: $kernel"
else
        echo "There is a new kernel. You need a reboot..."
        echo "Current kernel: $kernel"
        echo "The latest kernel: $latest"
        echo "$sdate\nCurrent kernel: $kernel\nLatest kernel: $latest"
        echo "Sleeping for $sdelay seconds..."
        sleep $sdelay
        echo "Waking up and rebooting..."
        /sbin/reboot
fi