Redirect

Hi. i am using MT 3.14 like a pptp server. I need to redirect ALL active pptp-conections at the beginning of the month on custom page. Is it posiible?
I did this one: /ip firewall nat add action=dst-nat chain=dstnat dst-port=80 protocol=tcp to-addresses=xxx.xxx.xxx.xxx to-ports=80.
But i need something like TTL (20-40 secs) for 1-3 times per month.