That is not true. If L4 missions, even vs faction ships, would give you 55 milions in 5 minutes, no one do anything else for ISK generation. With all warping, looting, shooting etc you are good if you get 55 milions per hour, not per 5 minutes.
If you are lucky with burner missions, you can get more, much more, but still not 12 x 55 = 660 milions per hour. For short amount of time you can focus on blitzing, to get about 100 milions per hour, but than you will have slow time to get your standings back.