My suggestion for a time function

time_ago.php

<?php

if ( ! function_exists('time_ago'))
{
	function time_ago($time, $max_units = NULL)
	{
		$lengths = array(1, 60, 3600, 86400, 604800, 2630880, 31570560, 315705600);
		$units = array('second', 'minute', 'hour', 'day', 'week', 'month', 'year', 'decade');
		$unit_string_array = array();
	
		$max_units = (is_numeric($max_units) && in_array($max_units, range(1,8))) ? $max_units : sizeOf($lengths);
		$diff = (is_numeric($time) ? time() - $time : time() - strtotime($time));
		$future = ($diff < 0) ? 1 : 0;
		$diff = abs($diff); // Let's get positive!
		
		$total_units = 0;
		for ($i = sizeOf($lengths) - 1; $i >= 0; $i--)
		{
			if ($diff > $lengths[$i] && $total_units < $max_units)
			{
				$amount = floor($diff / $lengths[$i]);
				$mod = $diff % $lengths[$i];
				
				$unit_string_array[] = $amount . ' ' . $units[$i] . (($amount == 1) ? '' : 's');
				$diff = $mod;
				$total_units++;
			}
		}
		
		return ($future) ? implode($unit_string_array, ', ') . ' to go' : implode($unit_string_array, ', ') . ' ago';
	}
}

// 3 seconds ago
echo time_ago(time() - 3) . "<br />";

// 1 minute, 30 seconds ago
echo time_ago(time() - 90, 'invalidparam') . "<br />";

// 3 minutes ago
echo time_ago(time() - 180) . "<br />";

// 1 hour, 30 minutes, 6 seconds ago
echo time_ago(time() - 3604 * 1.5) . "<br />";

// 3 hours, 9 seconds ago
echo time_ago(time() - 3603 * 3) . "<br />";

// 1 day, 1 hour, 50 seconds ago
echo time_ago(time() - 3602 * 25) . "<br />";

// 5 days (note the 2nd param)
echo time_ago(time() - 3601 * 24 * 5, 1) . "<br />";

// Depends on when you run the script :)
echo time_ago('Thursday, August 25, 23:00') . "<br />";

// 33 seconds to go
echo time_ago(time() + 343) . "<br />";

// 1 month, 2 weeks, 5 days to go (note the 2nd param)
echo time_ago(time() + 36201 * 24 * 5, 3) . "<br />";

time_ago_plural.php

<?php

if ( ! function_exists('time_ago'))
{
	function time_ago($time, $max_units = NULL)
	{
		$lengths = array(1, 60, 3600, 86400, 604800, 2630880, 31570560, 315705600);
		$units = array('second', 'minute', 'hour', 'day', 'week', 'month', 'year', 'decade');
		$units_plural = array('seconds', 'minutes', 'hours', 'days', 'weeks', 'months', 'years', 'decades');
		$unit_string_array = array();
	
		$max_units = (is_numeric($max_units) && in_array($max_units, range(1,8))) ? $max_units : sizeOf($lengths);
		$diff = (is_numeric($time) ? time() - $time : time() - strtotime($time));
		$future = ($diff < 0) ? 1 : 0;
		$diff = abs($diff); // Let's get positive!
		
		$total_units = 0;
		for ($i = sizeOf($lengths) - 1; $i >= 0; $i--)
		{
			if ($diff > $lengths[$i] && $total_units < $max_units)
			{
				$amount = floor($diff / $lengths[$i]);
				$mod = $diff % $lengths[$i];
				
				$unit_string_array[] = $amount . ' ' . (($amount == 1) ? $units[$i] : $units_plural[$i]);
				$diff = $mod;
				$total_units++;
			}
		}
		
		return ($future) ? implode($unit_string_array, ', ') . ' to go' : implode($unit_string_array, ', ') . ' ago';
	}
}

// 3 seconds ago
echo time_ago(time() - 3) . "<br />";

// 1 minute, 30 seconds ago
echo time_ago(time() - 90, 'invalidparam') . "<br />";

// 3 minutes ago
echo time_ago(time() - 180) . "<br />";

// 1 hour, 30 minutes, 6 seconds ago
echo time_ago(time() - 3604 * 1.5) . "<br />";

// 3 hours, 9 seconds ago
echo time_ago(time() - 3603 * 3) . "<br />";

// 1 day, 1 hour, 50 seconds ago
echo time_ago(time() - 3602 * 25) . "<br />";

// 5 days (note the 2nd param)
echo time_ago(time() - 3601 * 24 * 5, 1) . "<br />";

// Depends on when you run the script :)
echo time_ago('Thursday, August 25, 23:00') . "<br />";

// 33 seconds to go
echo time_ago(time() + 343) . "<br />";

// 1 month, 2 weeks, 5 days to go (note the 2nd param)
echo time_ago(time() + 36201 * 24 * 5, 3) . "<br />";