how do i get a greeting for logged in uses by the time of day

hi i am looking to combing to pieces of code into 1 both work but not together keep no matter what i try it keeps crashing the site

<?php
$t=date("H");
 if ($t<"12")
   {
   echo " Have a good morning!  $display_name ";
   }
 else if ($t<"18")
   {
   echo " Have a good afternoon!   $display_name ";
   }
else
{
   echo " Have a good evening!   $display_name ";
   } ?>

and

<?php global $current_user; wp_get_current_user(); ?>
<?php if ( is_user_logged_in() ) { 
 echo 'Welcome Brother: ' . $current_user->user_login . "\n";  } 
else { wp_loginout(); } ?>

other user parameters would be great to swap out

I can see two very obvious flaws that might be holding you back.

$t=date("H"); gives you a formatted date as a string while if ($t<"12") and else if ($t<"18") are trying to do maths on words.

Consider $t=(int)date("H"); (force the answer to be a whole number) with if ($t<12) and else if ($t<18) which at least does maths with numbers.