Hi,I did this a while back,BA to KEF and back in ET,about 3 hours,if you come back ET after security at KEF they have large display buckets full if miniatures of alcohol,grab some there for your flight back!!! I had all my trips in Iceland cancelled as the weather was so bad,but I had a great time,was there for 3 days,and was never bored,but it is expensive,so beware of that,the road to/from the airport is through old lava fields,have a great time....