Rolling expiration with WordPress Transients: Each time the transient is accessed the expiration is delayed. Intended for rate-limiting (be careful not to share a transient btw multiple users). Might work better for micro-caching in the event a flood is n

WP_rolling_transient.php

$call_limit = 350; // API calls (in an hour)
$time_limit = 60 * 60; // 1 hour (in seconds)
$transient_name = $host  . "_rate_limit"; // Using their host name as the unique identifier

// Check to see if there are any transients that match the name, if not create a new one
if ( false === ( $calls = get_transient( $transient_name ) ) ) {
	$calls[] = time();
	set_transient( $transient, $calls, $time_limit ); // Use an array of time() stamps for rolling effect
} else {
	// There is already a transient with this name
	$calls[] = time(); // Add a new time() stamp to the $calls array
	set_transient( $transient, $calls, $time_limit ); // Reset the transient (w/ expiration time)

	$call_count = count( $calls ); // How many calls have been made

	if ( $call_limit < $call_count ) { // If we're over the call limit, remove expired timestamps
		// Shift time from first element of array
		while ( $call = array_shift( $calls ) ) {
			// If time is >= current time - time limit, then it belongs in the array
			// Add it back and reset the transient
			if ( $call >= ( time() - $time_limit ) ) {
				array_unshift( $calls, $call );
				set_transient( $transient, $calls, $time_limit );
				break; // Stop processing, we're within the time_limit time now.
			}
		}

		// If we're still over the call limit, they've made too many requests in the time limit
		if ( $call_limit <= count( $calls ) ) {
			// The session needs to be killed
			die('Error: You have exceeded your rate limit for API calls, only ' . $call_limit . ' API calls are allowed every ' . $time_limit . ' seconds.');
		}
	}
}