I believe the two airfields other than that of departure and landing have to be at least 50nm apart. I am pretty sure you have to do it in one day.
To clarify you have to fly from A to B to C to A. B and C must be 50nm apart or greater and total straight line distance bewteen A,B, C and A must be 300nm or greater.
What I dont know is if they accept A,B C to D. Never mind, I've done mine anyway.