Help with a PHP script to convert time

[Anon]

                        I am writing a script in PHP that will convert time and I am having trouble updating the database again once the
                        calculations are done.

                        Could someone have a look at the script and see if I am headed in the right direction??

                        Please see below for more details.

                        <?php

                        # Connect to MySQL

                        $link = mysql_connect($hostname, $username, $password)
                        or die("Could not connect to database<br>\n");

                        # Select correct database within MySQL and select time fields needed

                        mysql_select_db("charman_timesheets", $link)
                        or die("Could not select the correct database");

                        $start_time = mysql_query("select start_time from charman_timesheets");
                        $stop_time = mysql_query("select stop_time from charman_timesheets");

                        # Split times needed into minutes to create total time


                        function start_time_calc($start_time)
                        {
                        if (strstr($start_time, ':'))
                        {
                        # Split hours and minutes.
                        $separatedData1 = split(':', $start_time);

                        $minutesInHours1 = $separatedData1[0] * 60;
                        $minutesInDecimals1 = $separatedData1[1];

                        $totalMinutes1 = $minutesInHours1 + $minutesInDecimals1;
                        }
                        else
                        {
                        $totalMinutes1 = $start_time * 60;
                        }

                        return $totalMinutes1;
                        }

                        function stop_time_calc($stop_time)
                        {
                        if (strstr($stop_time, ':'))
                        {
                        # Split hours and minutes.
                        $separatedData2 = split(':', $stop_time);

                        $minutesInHours2 = $separatedData2[0] * 60;
                        $minutesInDecimals2 = $separatedData2[1];

                        $totalMinutes2 = $minutesInHours2 + $minutesInDecimals2;
                        }
                        else
                        {
                        $totalMinutes2 = $stoptime * 60;
                        }

                        return $totalMinutes2;


                        }

                        $total_time = $totalMinutes2 - $totalMinutes1

                        $total_time2 = $total_time / 60

                        $query = "UPDATE charman_timesheets SET total_time='$totaltime2' WHERE (total_time='00:00')";

                        $result = mysql_query($query2);


                        ?>