date_range_parse.function.php

<?php
function range_parse($date, $default_year) {
	$get_month_num = function($month_name) {
		$month_num = false; //default

		for($i=1; $i <= 12; $i++) {
			$month_start = mktime(12,0, 0, $i, 1);
			$month_long = date('F', $month_start);
			$month_short = date('M', $month_start);
			$month_long = mb_strtolower($month_long);
			$month_short = mb_strtolower($month_short);

			if(
				mb_stripos($month_name, $month_long) === 0 ||
				mb_stripos($month_name, $month_short) === 0
			) {
				//pop off month then try to parse year and day
				$month_num = $i;
				break;
			}
		}

		return $month_num;
	};

	$to_full_year = function($year, $split_point = 65) {
		if(
			$year < 100 &&
			$year >= $split_point
		) {
			$year = "19$year";
		} elseif(
			$year >= 0 &&
			$year < $split_point
		) {
			$year = "20$year";
		}

		return $year;
	};

	$strip_empty = function(array $array){
		$stripped = array_filter($array, function($el) {
			return ($el ==  '') ? false : true;
		});
		$stripped = array_values($stripped);

		return $stripped;
	};

	$date = trim($date);
	$date = mb_strtolower($date);

	$range = new stdClass;

	$month_names = [];
	for($i=1; $i <= 12; $i++) {
		$month_start = mktime(12,0, 0, $i, 1);
		$month_long = date('F', $month_start);
		$month_short = date('M', $month_start);
		$month_names[] = mb_strtolower($month_long);
		$month_names[] = mb_strtolower($month_short);
	}
	$months_or = implode('|', $month_names);

	if( //month
		preg_match("/^($months_or)\s*(,|\s)\s*0*((19|20)[0-9]{2})$/", $date) || // jan ,yyyy
		preg_match("/^($months_or)\s*,\s*0*([0-9]{2})$/", $date) || // jan ,yy
		preg_match("/^($months_or)$/", $date) // jan
	) {
		$date = preg_replace('/(,|\s)/', ' ', $date);
		$date = explode(' ', $date);
		$date= $strip_empty($date);
		$date = array_pad($date, 2, '');
		list($month, $year) = $date;
		$month = ctype_digit($month) ? $month : $get_month_num($month);
		$year = ($year == '') ? $default_year : $year;
		$year = $to_full_year($year);

		$start = mktime(0, 0, 0, $month, 1, $year);
		$days_in_month = date('t', $start);
		$month_length = $days_in_month * 24 * 60 * 60;

		$range->type = 'month';
		$range->formatted = date('F, Y', $start);
		$range->start = $start;
		$range->length = $month_length;
		$range->end = $range->start + $range->length;
	} elseif( //day
		preg_match("/^0*(1[0-2]|[1-9])\/0*(3[0-1]|[1-2][0-9]|[1-9])\/0*((19|20)?[0-9]{2})$/", $date) || // m/d/y
		preg_match("/^($months_or)\s0*(3[0-1]|[1-2][0-9]|[1-9])\s*(,|\s)\s*0*((19|20)?[0-9]{2})$/", $date) || // jan 03, y
		preg_match("/^0*(1[0-2]|[1-9])\/0*(3[0-1]|[1-2][0-9]|[1-9])$/", $date) || // mm/dd
		preg_match("/^($months_or)\s*0*(3[0-1]|[1-2][0-9]|[1-9])$/", $date) // jan dd
	) {
		$date = preg_replace('/(,|\s|\/)/', ' ', $date);
		$date = explode(' ', $date);
		$date = $strip_empty($date);
		list($month, $day, $year) = array_pad($date, 3, '');

		$month = ctype_digit($month) ? $month : $get_month_num($month);
		$year = ($year == '') ? $default_year : $year;
		$year = $to_full_year($year);
		// print_r_pre($year); exit;

		$valid = checkdate($month, $day, $year);
		if($valid) {
			$start = mktime(0, 0, 0, $month, $day, $year);

			$range->type = 'day';
			$range->formatted = date('F j, Y', $start);
			$range->start = $start;
			$range->length = 24 * 60 * 60;
			$range->end = $range->start + $range->length;
		} else {
			$range = false;
		}
	} elseif( //year
		preg_match("/^((19|20)?[0-9]{2})$/", $date) // y
	) {
		$year = date($date);
		$year = $to_full_year($year);

		$start = mktime(0, 0, 0, 1, 1, $year);
		$is_leap_year = date('L', $start);
		$days_in_year = $is_leap_year ? 366 : 365;
		$year_length = $days_in_year * 24 * 60 * 60;

		$range->type = 'year';
		$range->formatted = date('Y', $start);
		$range->start = $start;
		$range->length = $year_length;
		$range->end = $range->start + $range->length;
	} else {
		$range = false;
	}

	return $range;
}
?>

Accepted formats:

Day Formats:
March d, yyyy
March d,yyyy
March d yyyy
March d yy
March d,yy
March d,0000yy
March d,0000yyyy(leading zeros)
m/d/y
m/d
March d

Month Formats;
March
Mar
Mar yy
Mar yyyy

Year Formats:
yyyy
yy(leading zeros not supported here)

Case-insensitive. Full and 3 letter month formats supported. Leading zeros supported except with "yy" year format