499314 reminder or alert on page

so the query is set up to show the list of records where the status is equal to 'Activo' ok so theres a column date and a column time heres the link [login to view URL] user = test pass = test so lets say the case # 20110141 has a task to do that is due on 4/12/2011 at 14:00 so i need that 30 min before the due date an alert show up like a reminder saying, "30 min left to do that task" and then they will click ok or accept and the alert will disappear then 25 min before the due date the alert will show up again saying "25 min left to do the task..." if the deadline reaches to its time lets say it is 14:00 already and they didnt do the task then the alert will show up every two min saying that, two minutes passed to do the task... and so on until they do it, the way it is going to show they did the task is when they edit the record and remove the status "Activo". then they page will no longer displays the record. now my question is sometimes they are away from the computer lets say the task is at 14:00 but they went to lunch at 13:20 and theyre coming back at 14:20 the page is open when they come back are they going to see a bunch of alerts? or is it going to be a conflict? another think some record are updated from other pages so if there are new record on the page they will not show up until they refresh the page so i was thinking about putting an auto refres every 4 or 6 min. is this going to work? or is there another way to do it?