The user can input TO and FROM dates and times for an event. How do we display the event time nicely?

daterange.php

<?php

function daterange_range($starttime, $endtime = null) {
  $return = "";
  //set the endtime to the start time if there isn't an endtime provided
  $endtime = empty($endtime) ? $starttime : $endtime;
  //turn them into timestamps if they are not timestamps already
  $endtime = ((int)$endtime == $endtime && is_int($endtime))? $endtime:strtotime($endtime);
  $starttime = ((int)$starttime == $starttime && is_int($starttime))? $starttime:strtotime($starttime);
  //boolean values to prevent test duplication,
  //better names could possibly be chosen
  $same_time = ($starttime == $endtime);
  $time_present = daterange_timespresent($starttime, $endtime);
  $year_same = (date('Y', $starttime) == date('Y', $endtime));
  $month_same = (date('m', $starttime) == date('m', $endtime));
  $day_same = (date('d', $starttime) == date('d', $endtime));
  $time_same = (date('H:i', $starttime) == date('H:i', $endtime));

  //starttime and endtime are the same
  if ($same_time) {
    $return = date('F jS', $starttime);
    //time?
    if (date('g:ia', $starttime) != "12:00am") {
      $return .= date(' g:ia', $starttime);
    }
  } else {
    if (!$year_same && !$month_same && $time_present) {
      //different years, different months, times present
      //"November 6th 3:00pm, 2010 to February 12th 6:00pm, 2011"
      $return = date('F jS - g:ia, Y', $starttime) . " to " . date('F jS - g:ia, Y', $endtime);
    } else if (!$year_same && !$month_same && !$time_present) {
      //different years, different months, no times
      //"November 6th, 2010 to February 12th, 2011"
      $return = date('F jS, Y', $starttime) . " to " . date('F jS, Y', $endtime);
    } elseif ($year_same && !$month_same && $time_present) {
      //different months, times present
      //"January 6th 3:00pm to February 12th 6:00pm"
      $return = date('F jS - g:ia', $starttime) . " to " . date('F jS - g:ia', $endtime);
    } elseif ($year_same && !$month_same && !$time_present) {
      //different months, no times
      //"January 6th to February 12th"
      $return = date('F jS', $starttime) . " to " . date('F jS', $endtime);
    } elseif ($year_same && $month_same && !$day_same && $time_present) {
      //same month, different days, times present
      //"January 6th 3:00pm to January 12th 6:00pm"
      $return = date('F jS - g:ia', $starttime) . " to " . date('F jS - g:ia', $endtime);
    } elseif ($year_same && $month_same && !$day_same && !$time_present) {
      //same month, different days, no times
      //"January 6th to 12th"
      $return = date('F jS', $starttime) . " to " . date('jS', $endtime);
    } elseif ($year_same && $month_same && $day_same && $time_present) {
      //times present, same day
      //"January 6th - 3:00pm - 6:00pm"
      $return = date('F jS - g:ia', $starttime) . " to " . date('g:ia', $endtime);
    } elseif ($year_same && $month_same && $day_same && !$time_present) {
      //same day, no times
      //"January 6th"
      $return = date('F jS');
    }
  }
  if (($year_same) && date('Y', $starttime) != date('Y')) {
    //Both the same year (or endtime is null), but not this year? Append the year
    //", 2012"
    $return .= date(', Y', $starttime);
  }
  return $return;
}

function daterange_timespresent($starttime, $endtime) {
  if (date('g:ia', $starttime) == "12:00am" && date('g:ia', $endtime) == "12:00am") {
    return false;
  }
  return true;
}

I suppose they make sense, you might want to make the second time optional though date_range('Jan 6', 'Jan 6') would be kind of annoying, also you called it daterange_range

originially started as a custom Drupal module, hence the strange function name. Good idea to make second param optional.

Ah, that makes sense... I agreen with @peterjanes I'd want date-time (e.g. "Jan. 6, 2010 3:00pm") rather than time-date.

Going for readability, it's a good point to raise. "3:00pm on January 6th, 2010 to 6:00pm on February 12th, 2011" is kindof annoying no matter how you slice it.

Untested, but here it is. Lots of IFs!

Merged @SeanJA's updates and changed some of the formats to be more readable.