Determine If Business Is Open/Closed Based On Business Hours

You would first need to create an array which will hold your days of the week, and their respective close/open time range(s).

/**
 * I setup the hours for each day if they carry-over)
 * everyday is open from 09:00 AM - 12:00 AM
 * Sun/Sat open extra from 12:00 AM - 01:00 AM
 */
$storeSchedule = [
    'Sun' => ['12:00 AM' => '01:00 AM', '09:00 AM' => '12:00 AM'],
    'Mon' => ['09:00 AM' => '12:00 AM'],
    'Tue' => ['09:00 AM' => '12:00 AM'],
    'Wed' => ['09:00 AM' => '12:00 AM'],
    'Thu' => ['09:00 AM' => '12:00 AM'],
    'Fri' => ['09:00 AM' => '12:00 AM'],
    'Sat' => ['12:00 AM' => '01:00 AM', '09:00 AM' => '12:00 AM']
];

You then loop over the current day's time range(s) and check to see if the current time or supplied timestamp is within a range. You do this by using the DateTime class to generate a DateTime object for each time range's start/end time.

The below will do this and allow you to specify a timestamp in case you are wanting to check a supplied timestamp instead of the current time.

// current or user supplied UNIX timestamp
$timestamp = time();

// default status
$status = 'closed';

// get current time object
$currentTime = (new DateTime())->setTimestamp($timestamp);

// loop through time ranges for current day
foreach ($storeSchedule[date('D', $timestamp)] as $startTime => $endTime) {

    // create time objects from start/end times
    $startTime = DateTime::createFromFormat('h:i A', $startTime);
    $endTime   = DateTime::createFromFormat('h:i A', $endTime);

    // check if current time is within a range
    if (($startTime < $currentTime) && ($currentTime < $endTime)) {
        $status = 'open';
        break;
    }
}

echo "We are currently: $status";

See DEMO of above

Modified from the accepted answer for use on a AWS Debian Server (located on the west coast) where our store hours are actually EST... also dropped into a PHP function.

/*
 * decide based upon current EST if the store is open
 *
 * @return bool
 */
function storeIsOpen() {
    $status = FALSE;
    $storeSchedule = [
        'Mon' => ['08:00 AM' => '05:00 PM'],
        'Tue' => ['08:00 AM' => '05:00 PM'],
        'Wed' => ['08:00 AM' => '05:00 PM'],
        'Thu' => ['08:00 AM' => '05:00 PM'],
        'Fri' => ['08:00 AM' => '05:00 PM']
    ];

    //get current East Coast US time
    $timeObject = new DateTime('America/New_York');
    $timestamp = $timeObject->getTimeStamp();
    $currentTime = $timeObject->setTimestamp($timestamp)->format('H:i A');

    // loop through time ranges for current day
    foreach ($storeSchedule[date('D', $timestamp)] as $startTime => $endTime) {

        // create time objects from start/end times and format as string (24hr AM/PM)
        $startTime = DateTime::createFromFormat('h:i A', $startTime)->format('H:i A');
        $endTime = DateTime::createFromFormat('h:i A', $endTime)->format('H:i A');

        // check if current time is within the range
        if (($startTime < $currentTime) && ($currentTime < $endTime)) {
            $status = TRUE;
            break;
        }
    }
    return $status;
}

You should regroup all opening hours in a array since the openings hours of yesterday could be of influence if you stay opened after midnight. Also having the possibility to have several opening hours per day might be handy.

<?php

$times = array(
    'mon' => '9:00 AM - 12:00 AM',
    'tue' => '9:00 AM - 12:00 AM',
    'wed' => '9:00 AM - 12:00 AM',
    'thu' => '9:00 AM - 12:00 AM',
    'fri' => '9:00 AM - 1:00 AM',
    'sat' => '9:00 AM - 1:00 PM, 2:00 PM - 1:00 AM',
    'sun' => 'closed'
);

function compileHours($times, $timestamp) {
    $times = $times[strtolower(date('D',$timestamp))];
    if(!strpos($times, '-')) return array();
    $hours = explode(",", $times);
    $hours = array_map('explode', array_pad(array(),count($hours),'-'), $hours);
    $hours = array_map('array_map', array_pad(array(),count($hours),'strtotime'), $hours, array_pad(array(),count($hours),array_pad(array(),2,$timestamp)));
    end($hours);
    if ($hours[key($hours)][0] > $hours[key($hours)][1]) $hours[key($hours)][1] = strtotime('+1 day', $hours[key($hours)][1]);
    return $hours;
}

function isOpen($now, $times) {
    $open = 0; // time until closing in seconds or 0 if closed
    // merge opening hours of today and the day before
    $hours = array_merge(compileHours($times, strtotime('yesterday',$now)),compileHours($times, $now)); 

    foreach ($hours as $h) {
        if ($now >= $h[0] and $now < $h[1]) {
            $open = $h[1] - $now;
            return $open;
        } 
    }
    return $open;
}

$now = strtotime('7:59pm');
$open = isOpen($now, $times);

if ($open == 0) {
    echo "Is closed";
} else {
    echo "Is open. Will close in ".ceil($open/60)." minutes";
}

?>

On the other hand if you only want to resolve the problem with time like 9am - 5am you should check if $from > $to and add 1 day to $to if necessary.