How to show certain data on certain interval of period

Here’s a function you can put in functions.php.

function get_current_event() {
    global $post;
    $now = get_the_time('U');
    $year = get_the_time('Y');
    if($now >= strtotime("January 1 $year") && $now < strtotime("March 1 $year")) {
       return get_post_meta($post->ID,'eventA',true);
    }
    if($now >= strtotime("March 1 $year") && $now < strtotime("October 15 $year")) {
        return get_post_meta($post->ID,'eventB',true);
    }
    $nextyear = $year+1;
    if($now >= strtotime("October 15 $year") && $now < strtotime("January 1 $nextyear")) {
        return get_post_meta($post->ID,'eventC',true);
    }
    return false;
}

Then you can put this in your template:

print get_current_event();