Here may be a way. I used a file called "test.html" for the test:
/ip hotspot user profile set X advertising=yes advertise-interval=10m
/ip hotspot user profile set X advertising-url=
http://192.168.0.1/test.html
Replace X's with the profile line number and the advertising-url with the IP of your MT box. Mine is 192.168.0.1.
It will popup only when the user navigates from one page to another after 10 minutes. If the user stays on one page, the advertising popup sequence does not activate without the status page.
Upload a file "test.html" into the hotspot directory of your MT box. The servelet section in the hotspot docs should help with the variables you may need.