Even in severe turbulence ie much much worse than encountered near a large jet in take off or approach configuration, a helicopter remains perfectly controllable and has no desire to flip upside down. It might wobble a bit but it doesn't stall or spin.
After nearly 40 years of helicopter flying both mil and civil, mixing it with the big stuff when required, I have never been affected by wake turbulence from a FW.
A 3 min separation from a heavy jet is just massive overkill.