That line is in function AddDate ( $month, $day, $year, $numdays) {
$nday = $day + $numdays;
$newdate = mktime (0,0,0,$month,$nday,$year);
return getdate($newdate);
}
which is called by the following lines:
Line 383: $ndate = AddDate($mo, $da, $yr, -1);
Line 386: $ndate = AddDate($mo, $da, $yr, -7);
Line 389: $ndate = AddDate($mo, $da, $yr, -30);
Line 392: $ndate = AddDate($mo, $da, $yr, -365);
Line 471: $ndate = AddDate($mo, $da, $yr, +1);
Line 474: $ndate = AddDate($mo, $da, $yr, +7);
Line 477: $ndate = AddDate($mo, $da, $yr, +30);
Line 480: $ndate = AddDate($mo, $da, $yr, +365);
Line 1004: $tdate = AddDate($pmo, $pda, $pyr, 0); // just to get the name of the day
With the data you provided, I can't tell which of those may have been the issue.. sorry.
Do you have the access_log for the page showing the URL used (with the arguments) for 20-Apr-2020 07:39:43 ? I'd need to see that to debug further.