Again, before you sleep combine for example:
Argan oil feet / heels moisturization massage
And putting on a pair of clean, soft and warm cotton socks.
This will allow the Argan oil to seep into the cracked heels (and feet in general) overnight.
It will thus enhance the desired effect tremendously and you should see pleasing results in no time.
Repeat (nightly) as needed.
Alternatively, you can also use pure Argan oil as described above, during day.
Depending on the dryness of your feet, you can apply pure Argan oil 2 till 3 times a day.
You´ll want to gently and lavishly massage it into the affected areas including toes, nails and cracked heels to restore the natural moisture.