Interesting point. What exactly is attached to pins 6 and 7? If it's a conventional RC receiver then it shouldn't be a problem as the servo pulse will continually repeat approx every 20ms...so very little waiting involved.
I've used that basic mechanism for 6 channels with no problems. But the pulses are roughly 1000 to 2000 microseconds. Subtracting 30 from 2000 isn't going to give you anything in degrees.
Steve