it will redirect automatically but it may not be as smooth as you think, in order to get redirected client must sends a TCP SYN to the URL's IP address, then the AP replies back on behalf of the site with TCP SYN ACK. After that, the client sends the HTTP GET and then AP intercepts it and responds back with a splash page.
This process may not happen in the middle of a transaction smoothly, but it will happen eventually, may take few seconds.
best it to increase splash frequency to may be a day or a week, so that clients are not interrupted.
