vShow increments by one every vDelay seconds up to vSheets, where it starts at 1 again. 86400 is the number of seconds in a day, so this is converting the time portion of now() to seconds after midnight. The calculation is then done in seconds.
Logic will get you from a to b. Imagination will take you everywhere. - A Einstein
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.