change
$hours .= '<option value="'.check($i).'">'.$i.'</option>'."\n";
to
$hours .= '<option value="'.check($i).'"';
if (date("g",time())==$i) { $hours .= " selected"; }
$hours .= '>'.$i.'</option>'."\n";
likewise, the minutes become:
$minutes .= '<option value="'.check($i).'"';
if (date("i",time())==$i) { $minutes .= " selected"; }
$minutes .= '>'.check($i).'</option>'."\n";