I think this must have been solved many times here on WordPress Answers.

You could also check out the examples in the Time parameters part in Codex for WP_Query.

Here are two of them (slightly modified to your needs)

Example 1:

// Create a new filtering function that will add our where clause to the query
function filter_where( $where = '' ) {
    // posts in the last 7 days
    $where .= " AND post_date > '" . date('Y-m-d', strtotime('-7 days')) . "'";
    return $where;
}

add_filter( 'posts_where', 'filter_where' );
$slider_query = new WP_Query('posts_per_page=5&cat=3&orderby=highest_rated&order=desc');    
remove_filter( 'posts_where', 'filter_where' );

Example 2:

// Create a new filtering function that will add our where clause to the query
function filter_where( $where = '' ) {
    // posts for May 1 to March 8, 2013
    $where .= " AND post_date >= '2013-05-01' AND post_date < '2013-05-8'";
    return $where;
}

add_filter( 'posts_where', 'filter_where' );
$slider_query = new WP_Query('posts_per_page=5&cat=3&orderby=highest_rated&order=desc');
remove_filter( 'posts_where', 'filter_where' )

I think this must have been solved many times here on WordPress Answers.

You could also check out the examples in the Time parameters part in Codex for WP_Query.

Here are two of them (slightly modified to your needs)

Example 1:

// Create a new filtering function that will add our where clause to the query
function filter_where( $where = '' ) {
    // posts in the last 7 days
    $where .= " AND post_date > '" . date('Y-m-d', strtotime('-7 days')) . "'";
    return $where;
}

add_filter( 'posts_where', 'filter_where' );
$slider_query = new WP_Query('posts_per_page=5&cat=3&orderby=highest_rated&order=desc');    
remove_filter( 'posts_where', 'filter_where' );

Example 2:

// Create a new filtering function that will add our where clause to the query
function filter_where( $where = '' ) {
    // posts for May 1 to March 8, 2013
    $where .= " AND post_date >= '2013-05-01' AND post_date < '2013-05-8'";
    return $where;
}

add_filter( 'posts_where', 'filter_where' );
$slider_query = new WP_Query('posts_per_page=5&cat=3&orderby=highest_rated&order=desc');
remove_filter( 'posts_where', 'filter_where' )

assuming that you have this orderby=highest_rated covered with some plugin as you describe in the comment above.