I just put them in a plastic tub full of kitty litter. Not the "clumping kind, just the "oil dry" kind.
How long do you leave them in the clay? This something I have not heard of and sounds interesting.
About salt, sometimes it can draw moisture enough from the air to spoil a hide months later.
>>edit: I have not used salt for a long time and forgot to mention, salt only gets stuff semi dry and can let skin rot to complete the dying process alum should added in roughly equal amounts to the salt.
I personally never use salt on a pelt, they last just as long simply air dried and are preserved better with borax. In dealing with pelts for the international fur market salt is a no-no because of various problems it causes.
How long does it take; in optimum conditions -just air no chemicals, temperatures 50-70F, RH<80, fan to circulate air- about a week to air dry a raccoon or coyote pelt, longer for beaver and less for fox or bobcat. this will make it dry enough to ship through the USPS and store for several months- for long term storage of a pelt it needs to be in cold storage or bug proofed.
If the bone is left in a tail I would keep it in a shoe box of borax about a week.