Example abstraction that only allows a resolution of "day" for time inside a specific business domain

Day.php

<?php

declare(strict_types=1);

namespace Core\Domain\Time;

use DateTimeImmutable;
use DateTimeZone;
use Generator;
use Iterator;
use function sprintf;
use Webmozart\Assert\Assert;

/** @psalm-immutable */
final class Day
{
    public const FORMAT = '/^(\d{4})-(\d{2})-(\d{2})$/';

    /** @var string */
    private $date;

    private function __construct(string $date)
    {
        $this->date = $date;
    }

    /**
     * @param string $date in format YYYY-mm-dd
     *
     * @see Day::FORMAT
     *
     * @psalm-pure
     */
    public static function fromDateString(string $date): self
    {
        Assert::regex($date, self::FORMAT);

        $dateObject = DateTimeImmutable::createFromFormat('Y-m-d', $date, new DateTimeZone('UTC'));

        Assert::object($dateObject, sprintf('Given date "%s" does not appear to be a valid date', $date));
        Assert::same($date, $dateObject->format('Y-m-d'), sprintf('Given date "%s" does not appear to be a valid date', $date));

        return new self($date);
    }

    public static function fromDate(DateTimeImmutable $date): self
    {
        return new self($date->format('Y-m-d'));
    }

    public function equals(self $other): bool
    {
        return $other->date === $this->date;
    }

    public function isAfter(self $other): bool
    {
        return $this->toDateTimeImmutable() > $other->toDateTimeImmutable();
    }

    public function toDateTimeImmutable(): DateTimeImmutable
    {
        $dateObject = DateTimeImmutable::createFromFormat('Y-m-d H:i:s.u', $this->date.' 00:00:00.0', new DateTimeZone('UTC'));

        Assert::object($dateObject);

        return $dateObject;
    }

    public function toString(): string
    {
        return $this->date;
    }
}