I think everyone agrees that a visit to Islay should last as long as possible but if you just don't have the time you can do Islay in one day. Agreed, you don't get to see as much as you should but on the other hand, you'll probably get good enough impressions to start thinking about a return visit. The video below gives an example of what you could do when you are one day on Islay. If I'm not mistaken the person in this video travelled with Scottish Routes and they visited Bruichladdich, Kilchoman and Bowmore distilleries as well as Machir Bay and the Islay Woolen Mill. Enjoy!