The cabe makes bifilar winding, so it has no effect on signal on the wire. Its task is to cancel currents oscillating from motor, to receiver and servos, what makes dipol long enough for wawes on MHZ frequencies, It has almost no effect if you have only timer on end of that cable.

It takes a lot less noise to bother a radio than it does to bother something like a Hubin timer

Tim
I think you got this backwards based on the other stuff you said.  I agree and I would add Will Hubin seem to think it would make no difference with his timer.  I passed this by him first before posting it here.  Will suggested I post it here.

Igor, if I understood you correctly you don't believe it affects RFI, but is there for current stability from variations in the current load caused by the motor. I can't see any difference in operation with or without the donut.  But I don't have a scope to look at the +V wire on the servo lead.  It would be interesting to see what the +V and for that matter the ground look like when the motor is running.
Andy

No Andy, I mean it does NOT make any effect for current in wires in meaning supply for receiver, timer or so. The winding is bifilar, means the current going from ESC through red wire to supply the rest of the system (receiver, servos etc, or timer in our case), goes also back through the black wire and they cancel the EMF in the nut each other. The nut is damping only currents going through all wires paralel, and it can be only noise induced from outside (motor, PWM switching, noise from moving metal parts etc) induced to long wire from motor to rest of the system connected on that servo cable. And since we have only one small timer, there is only low chance that something wrong will induce there and that it will be so strong that it needs damping.