PHP Unix Date Insert, Update

Unix Date

// Static

$checkIN      = $this->input->post('checkIN');
$checkIN = str_replace("/", "-", $checkIN);
$checkIN = date('Y-m-d h:i:s', strtotime($checkIN));

$checkOUT     = $this->input->post('checkOUT');
$checkOUT = str_replace("/", "-", $checkOUT);
$checkOUT = date('Y-m-d h:i:s', strtotime($checkOUT));


//Dynamic in for loop

$checkIN[$key]      = $this->input->post('checkIN')[$key];				
$checkIN[$key] = str_replace("/", "-", $checkIN[$key]);
$checkIN[$key] = date('Y-m-d h:i:s', strtotime($checkIN[$key]));

$checkOUT[$key]     = $this->input->post('checkOUT')[$key];
$checkOUT[$key] = str_replace("/", "-", $checkOUT[$key]);
$checkOUT[$key] = date('Y-m-d h:i:s', strtotime($checkOUT[$key]));

//GET Date with Format
<?php echo date('d-m-Y',strtotime($singlelistva['passenger_checkout']));?>