Activate Plugin Automatically After Set Time

Add this to the functions.php file of your active (child) theme-

add_action( 'init', 'wpse_393267_activate_plugin' );
function wpse_393267_activate_plugin() {

    if( !function_exists( 'is_plugin_active' ) ) {
        include_once ABSPATH . '/wp-admin/includes/plugin.php';
    }

    $plugin_to_activate="jetpack/jetpack.php"; // plugin-dir/plugin-file.php
    $date_to_activate="2021-08-13"; // YYYY-MM-DD

    if( is_plugin_active( $plugin_to_activate ) ) return;

    if( time() >= strtotime( $date_to_activate ) ) {
        activate_plugin( $plugin_to_activate );
    }
}

Change the $plugin_to_activate and $date_to_activate as you want.