A few skippers at a previous airline bent the SOP a bit and personally I liked it. Home base was notorious for >45 minute taxi out times in the winter, so they started all engines as per normal and then once on the taxi way on which the queue began to form, shut one down with a view to starting it up again once 4 or 5 aircraft were in front. Any SOP that wants you to consider it for a taxi time of less than 15 minutes is bean-counter bollocks that will ruin your day one day and should be ignored.