Error: Non-Numeric Value Encountered

fusion_get_settings('timeoffset') == Europe/Belgrade

 return strftime($format, $timestamp);

This is the original function

// Utility function to return a formatted local date
function localdate($format, $timestamp)
{
 global $settings;
 return strftime($format, $timestamp + $settings['timeoffset']*3600);
}

This my modified function

// Utility function to return a formatted local date
function localdate($format, $timestamp)
{
 global $settings;
   $format = showdate($settings['shortdate'], TIME, ['tz_override' => $settings['timeoffset']]);
 return strftime($format, $timestamp);
}

These are the 3 localdate calls in the script with locale define for strftime
Locale that defines strftime

$locale['AN010'] = '%a, %b %e at %H:%M'; // Date-format used for strftime(...)
$locale['AN011'] = '%e %b %H:%M';       // Short date-format used for strftime(...) in autonews_panel only

<td>".localdate($locale['AN010'], $date)."</td>
localdate($locale['AN010'], $data['timestamp']),
".localdate($locale['AN010'], $autonews_settings['ts_thissend'])."

$locale['AN010'] = '%a, %b %e at %H:%M'; // Date-format used for strftime(...)
$locale['AN011'] = '%e %b %H:%M'; // Short date-format used for strftime(...) in autonews_panel only

<td>".showdate($locale['AN010'], $date)."</td>
showdate($locale['AN010'], $data['timestamp']),
".showdate($locale['AN010'], $autonews_settings['ts_thissend'])."

function localdate($format, $timestamp) {
 return showdate($format, $timestamp);
}