Define the following variables:
Set vDelay = 15; // duration of screen in seconds
Set vSheets = 10; // number of sheets
Set vShow = =ceil((frac(now())*86400/(vSheets*vDelay)-floor(frac(now())*86400/(vSheets*vDelay)))*(vSheets));
(the double = sign is not a misprint)
Now for each sheet, set the conditionally show to
(vShow = 1) // for the first sheet
(vShow = 2) // for the next sheet
... and so on.
vShow is updated continuously and counts from 0 to vSheets-1, incrementing every vDelay seconds.
This approach should work in both the plugin and in Ajax.
How I have gone about this in the past is by having QlikView display in an iFrame and have an HTML timer refreshing the host page. The QlikView URL can then have a parameter to set a field value that fires a trigger to show the correct page.
See this post on Ajax parameters, and my comment on the third page around getting triggers to fire.
Hope that helps,