What are the date bounderies in PHP

I’d dare say that PHP date ranges do not have hard-coded limits, probably just the integer size or some similar platform limit. However, not all input mechanisms work the same way. For example:

$years = [
    -25000,
    0,
    9999,
    10000,
    25000,
];
foreach ($years as $year) {
    $dt1 = date_create_from_format('d/m/Y', "22/09/$year");
    $dt2 = new DateTime();
    $dt2->setDate($year, 9, 22);
    var_dump($year, $dt1, $dt2);
    echo "n";
}

int(-25000)
bool(false)
object(DateTime)#1 (3) {
  ["date"]=>
  string(28) "-25000-09-22 16:16:09.918321"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(13) "Europe/Berlin"
}

int(0)
object(DateTime)#2 (3) {
  ["date"]=>
  string(26) "0000-09-22 16:16:09.000000"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(13) "Europe/Berlin"
}
object(DateTime)#3 (3) {
  ["date"]=>
  string(26) "0000-09-22 16:16:09.918367"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(13) "Europe/Berlin"
}

int(9999)
object(DateTime)#1 (3) {
  ["date"]=>
  string(26) "9999-09-22 16:16:09.000000"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(13) "Europe/Berlin"
}
object(DateTime)#2 (3) {
  ["date"]=>
  string(26) "9999-09-22 16:16:09.918415"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(13) "Europe/Berlin"
}

int(10000)
bool(false)
object(DateTime)#1 (3) {
  ["date"]=>
  string(27) "10000-09-22 16:16:09.918451"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(13) "Europe/Berlin"
}

int(25000)
bool(false)
object(DateTime)#2 (3) {
  ["date"]=>
  string(27) "25000-09-22 16:16:09.918476"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(13) "Europe/Berlin"
}

In particular, date_create_from_format() reports this:

date_create_from_format('d/m/Y', "22/09/25000");
print_r(DateTime::getLastErrors());

Array
(
    [warning_count] => 0
    [warnings] => Array
        (
        )

    [error_count] => 1
    [errors] => Array
        (
            [10] => Trailing data
        )

)

This happens because, as documented, Y format code is:

A full numeric representation of a year, up to 4 digits

Regarding your specific code, it appears to work as expected:

function CheckFrDate($CheckDate){
    $BeginFrDate = date_create_from_format('d/m/Y', '22/09/1792');
    $EndFrDate = date_create_from_format('d/m/Y', '22/09/1806');
    if (
        $CheckDate->getTimestamp() > $BeginFrDate->getTimestamp() &&
        $CheckDate->getTimestamp() < $EndFrDate->getTimestamp()){
        return 1;
    }else{
        return -1;
    }
}

$CheckDate = date_create_from_format('d/m/Y', '23/09/1793');
var_dump(CheckFrDate($CheckDate));

int(1)

I no longer have a 32-bit Windows system to test but, if I recall correctly, DateTime interface was never affected by the 1970 Unix Epoch limit. However, if you use ->getTimestamp() to obtain a Unix timestamp, you’ll get an integer that will be.

You can drop Unix time altogether:

function CheckFrDate($CheckDate)
{
    $BeginFrDate = date_create_from_format('d/m/Y', '22/09/1792');
    $EndFrDate = date_create_from_format('d/m/Y', '22/09/1806');
    if ($CheckDate > $BeginFrDate && $CheckDate < $EndFrDate) {
        return 1;
    } else {
        return -1;
    }
}