how to call variable in php array

<?php
$tmRand = srand(floor(time() /60*30));
$x = array('"site.com/$user"','"site.com/$mail"');
$y = $x[array_rand($x)];
?>
<?php
for ($i = 0; $i <= 5; $i++) {
$user = "username";
$mail = "email";
$arr = array($y);
$url = $arr[array_rand($arr)];
echo "$url\n";
sleep(2);
}
$i++;

here I am trying a random url with the variable $user and $mail with time intervals per 30 minutes.

<?php
$tmRand = srand(floor(time() /60*30));
$x = array('"site.com/$user"','"site.com/$mail"');
$y = $x[array_rand($x)];
?>

output "site.com/$user" or "site.com/$mail"

from the results of the above output I try to randomly use a loop by calling the variable $y in array $arr = array($y); but the results that come out in the loop "site.com/$user" not "site.com/username"

<?php
for ($i = 0; $i <= 5; $i++) {
$user = "username";
$mail = "email";
$arr = array($y);
$url = $arr[array_rand($arr)];
echo "$url\n";
sleep(2);
}
$i++;