bootstrap.php

<?php

use Cake\I18n\Date;
use Cake\I18n\FrozenDate;
use Cake\I18n\FrozenTime;
use Cake\I18n\Time;

// Default config stuff

/*
 * Set default date & time for both mutable and immutable values
 */
$dateTimeToStringFormat = [
    IntlDateFormatter::MEDIUM,
    IntlDateFormatter::SHORT,
];
$dateToStringFormat = [
    IntlDateFormatter::SHORT,
    IntlDateFormatter::NONE,
];
$locale = 'nl-NL';

FrozenTime::setDefaultLocale($locale);
Time::setDefaultLocale($locale);
FrozenDate::setDefaultLocale($locale);
Date::setDefaultLocale($locale);

FrozenTime::setToStringFormat($dateTimeToStringFormat);
Time::setToStringFormat($dateTimeToStringFormat);
FrozenDate::setToStringFormat($dateToStringFormat);
Date::setToStringFormat($dateToStringFormat);

FrozenTime::$niceFormat = $dateTimeToStringFormat;
Time::$niceFormat = $dateTimeToStringFormat;
FrozenDate::$niceFormat = $dateToStringFormat;
Date::$niceFormat = $dateToStringFormat;

test.php

<?php

use Cake\I18n\Time;

$troubledTimeInstance = new Time();

debug($troubledTimeInstance);
debug(\Cake\I18n\Time::getDefaultLocale());
debug(\Cake\I18n\I18n::getLocale());
debug(\Cake\I18n\I18n::getDefaultLocale());