Transients APIを使う。
$transient = 'name';
if (false === ( $data = get_transient($transient) ) ) {
//期限切れ
$data = 'result';
set_transient($transient, $data, 60*60*1);
}
時間はWP3.5より下記定数が使える
MINUTE_IN_SECONDS = 60 (seconds)
HOUR_IN_SECONDS = 60 * MINUTE_IN_SECONDS
DAY_IN_SECONDS = 24 * HOUR_IN_SECONDS
WEEK_IN_SECONDS = 7 * DAY_IN_SECONDS
YEAR_IN_SECONDS = 365 * DAY_IN_SECONDS