mysql has a builtin profiler. You can enable profiling by issuing set profiling=1; and use show profiles; to get execution times.

if using PHP .. you can use microtime() before the query and after the query to figure out how long it took for the query to execute.

$sql_query='SELECT * FROM table';
$msc=microtime(true);
$mysql_query($sql_query);
$msc=microtime(true)-$msc;
echo $msc.' seconds'; // in seconds
echo ($msc*1000).' milliseconds'; // in millseconds

Try this...

mysql_query("SET profiling = 1;");
if (mysql_errno()) { die( "ERROR ".mysql_errno($link) . ": " . mysql_error($link) ); }

/* It goes without saying that this is your actual query that you want to measure the execution time of */
$query="SELECT some_field_name FROM some_table_name";
$result = mysql_query($query);
if (mysql_errno()) { die( "ERROR ".mysql_errno($link) . ": " . mysql_error($link) ); }

$exec_time_result=mysql_query("SELECT query_id, SUM(duration) FROM information_schema.profiling GROUP BY query_id ORDER BY query_id DESC LIMIT 1;");
if (mysql_errno()) { die( "ERROR ".mysql_errno($link) . ": " . mysql_error($link) ); }
$exec_time_row = mysql_fetch_array($exec_time_result);

echo "<p>Query executed in ".$exec_time_row[1].' seconds';