it could be heat soak but as you say that you let it cool down for a few mins i doubt a turbo timer is gonna help, fitting one can aslo invalidate your insurance as it i possable to leve your car runing and unatended just drive the last couple of miles off boost this should cool it down enough i did hear that on mid engined cars is is posable for the fuel to vaporise due to the heat maybe worth building a heat shield round the turbo