walled-garden ip dynamic entries.

Hi all,
I have a question.
I needed to whitelist https sites and what seemed to work best was using this solution presented here
http://wiki.mikrotik.com/wiki/Manual:IP/Hotspot/Walled_Garden
following the example:
“/ip hotspot walled-garden ip
add action=accept disabled=no dst-host=www.paypalobject.com

It worked, but it is dynamically adding entries to the Nat and firewall filters which is expected.

BUT,
I’ve done this for about 20 different hosts all with rotating IP’s and it seems like it’s generation over 3000 dynamic firewall entries.

If it keeps growing, will it crash the MT’s? and also if it will, is there a way to set a sort of “TTL” for a rule?

Thanks for any input.