Kromm in

I'd price things like this using Modifying Beings With One or Two Arms (p. B53): Point cost is equal to 1/10 of the percentile modifier per affected arm. In this case, the percentile modifier is -x% for Temporary Disadvantage (Weakness [-x]), so simply divide the value of Weakness by 10. This is essentially the model recommended in Cybernetics (p. B46) applied to the implicit advantage Arm [10]. You might also find some of the ideas under Undead Arm (Pyramid #3/1: Tools of the Trade – Wizards, p. 14) inspiring.

26 May 2017 Bruno said that Kromm suggested Reduced Time for both Weakness and Regeneration