About as long as is required to get a foam line set up. Most competent rescue companies should be able to have a foam line operational in well under two minutes from arrival if they have good access to the pool. Once the line is operational the bulk of the fire can be knocked down within 30 seconds or so. To make sure you get a nice solid blanket of foam to prevent reignition will probably take another minute or so. In total it should take about five minutes give or take.Of course something like an airport crash tender which is specifically set up to deal with this type of scenario should be able to use only one operator and get the fire under control in significantly less time than that.