function bp_core_time_since( $older_date, $newer_date = false ) {

	/**
	 * Filters whether or not to bypass BuddyPress' time_since calculations.
	 *
	 * @since 1.7.0
	 *
	 * @param bool   $value      Whether or not to bypass.
	 * @param string $older_date Earlier time from which we're calculating time elapsed.
	 * @param string $newer_date Unix timestamp of date to compare older time to.
	 */
	$pre_value = apply_filters( 'bp_core_time_since_pre', false, $older_date, $newer_date );
	if ( false !== $pre_value ) {
		return $pre_value;
	}

	/**
	 * Filters the value to use if the time since is unknown.
	 *
	 * @since 1.5.0
	 *
	 * @param string $value String representing the time since the older date.
	 */
	$unknown_text   = apply_filters( 'bp_core_time_since_unknown_text',   __( 'sometime',  'buddypress' ) );

	/**
	 * Filters the value to use if the time since is right now.
	 *
	 * @since 1.5.0
	 *
	 * @param string $value String representing the time since the older date.
	 */
	$right_now_text = apply_filters( 'bp_core_time_since_right_now_text', __( 'right now', 'buddypress' ) );

	/**
	 * Filters the value to use if the time since is some time ago.
	 *
	 * @since 1.5.0
	 *
	 * @param string $value String representing the time since the older date.
	 */
	$ago_text       = apply_filters( 'bp_core_time_since_ago_text',       __( '%s ago',    'buddypress' ) );

	// Array of time period chunks.
	$chunks = array(
		YEAR_IN_SECONDS,
		30 * DAY_IN_SECONDS,
		WEEK_IN_SECONDS,
		DAY_IN_SECONDS,
		HOUR_IN_SECONDS,
		MINUTE_IN_SECONDS,
		1
	);

	if ( !empty( $older_date ) && !is_numeric( $older_date ) ) {
		$time_chunks = explode( ':', str_replace( ' ', ':', $older_date ) );
		$date_chunks = explode( '-', str_replace( ' ', '-', $older_date ) );
		$older_date  = gmmktime( (int) $time_chunks[1], (int) $time_chunks[2], (int) $time_chunks[3], (int) $date_chunks[1], (int) $date_chunks[2], (int) $date_chunks[0] );
	}

	/**
	 * $newer_date will equal false if we want to know the time elapsed between
	 * a date and the current time. $newer_date will have a value if we want to
	 * work out time elapsed between two known dates.
	 */
	$newer_date = ( !$newer_date ) ? bp_core_current_time( true, 'timestamp' ) : $newer_date;

	// Difference in seconds.
	$since = $newer_date - $older_date;

	// Something went wrong with date calculation and we ended up with a negative date.
	if ( 0 > $since ) {
		$output = $unknown_text;

	/**
	 * We only want to output two chunks of time here, eg:
	 * x years, xx months
	 * x days, xx hours
	 * so there's only two bits of calculation below:
	 */
	} else {

		// Step one: the first chunk.
		for ( $i = 0, $j = count( $chunks ); $i < $j; ++$i ) {
			$seconds = $chunks[$i];

			// Finding the biggest chunk (if the chunk fits, break).
			$count = floor( $since / $seconds );
			if ( 0 != $count ) {
				break;
			}
		}

		// If $i iterates all the way to $j, then the event happened 0 seconds ago.
		if ( !isset( $chunks[$i] ) ) {
			$output = $right_now_text;

		} else {

			// Set output var.
			switch ( $seconds ) {
				case YEAR_IN_SECONDS :
					$output = sprintf( _n( '%s year',   '%s years',   $count, 'buddypress' ), $count );
					break;
				case 30 * DAY_IN_SECONDS :
					$output = sprintf( _n( '%s month',  '%s months',  $count, 'buddypress' ), $count );
					break;
				case WEEK_IN_SECONDS :
					$output = sprintf( _n( '%s week',   '%s weeks',   $count, 'buddypress' ), $count );
					break;
				case DAY_IN_SECONDS :
					$output = sprintf( _n( '%s day',    '%s days',    $count, 'buddypress' ), $count );
					break;
				case HOUR_IN_SECONDS :
					$output = sprintf( _n( '%s hour',   '%s hours',   $count, 'buddypress' ), $count );
					break;
				case MINUTE_IN_SECONDS :
					$output = sprintf( _n( '%s minute', '%s minutes', $count, 'buddypress' ), $count );
					break;
				default:
					$output = sprintf( _n( '%s second', '%s seconds', $count, 'buddypress' ), $count );
			}

			// Step two: the second chunk
			// A quirk in the implementation means that this
			// condition fails in the case of minutes and seconds.
			// We've left the quirk in place, since fractions of a
			// minute are not a useful piece of information for our
			// purposes.
			if ( $i + 2 < $j ) {
				$seconds2 = $chunks[$i + 1];
				$count2   = floor( ( $since - ( $seconds * $count ) ) / $seconds2 );

				// Add to output var.
				if ( 0 != $count2 ) {
					$output .= _x( ',', 'Separator in time since', 'buddypress' ) . ' ';

					switch ( $seconds2 ) {
						case 30 * DAY_IN_SECONDS :
							$output .= sprintf( _n( '%s month',  '%s months',  $count2, 'buddypress' ), $count2 );
							break;
						case WEEK_IN_SECONDS :
							$output .= sprintf( _n( '%s week',   '%s weeks',   $count2, 'buddypress' ), $count2 );
							break;
						case DAY_IN_SECONDS :
							$output .= sprintf( _n( '%s day',    '%s days',    $count2, 'buddypress' ), $count2 );
							break;
						case HOUR_IN_SECONDS :
							$output .= sprintf( _n( '%s hour',   '%s hours',   $count2, 'buddypress' ), $count2 );
							break;
						case MINUTE_IN_SECONDS :
							$output .= sprintf( _n( '%s minute', '%s minutes', $count2, 'buddypress' ), $count2 );
							break;
						default:
							$output .= sprintf( _n( '%s second', '%s seconds', $count2, 'buddypress' ), $count2 );
					}
				}
			}

			// No output, so happened right now.
			if ( ! (int) trim( $output ) ) {
				$output = $right_now_text;
			}
		}
	}

	// Append 'ago' to the end of time-since if not 'right now'.
	if ( $output != $right_now_text ) {
		$output = sprintf( $ago_text, $output );
	}

	/**
	 * Filters the English-language representation of the time elapsed since a given date.
	 *
	 * @since 1.7.0
	 *
	 * @param string $output     Final 'time since' string.
	 * @param string $older_date Earlier time from which we're calculating time elapsed.
	 * @param string $newer_date Unix timestamp of date to compare older time to.
	 */
	return apply_filters( 'bp_core_time_since', $output, $older_date, $newer_date );
}