It’s a good choice of essential oils you’ve decided to use, though I would go with Avocado oil instead of Castor oil. Avocado is richer in vitamin E and it is more popular in treatments for stretch marks and skin firmness. Usually, skin applications take a longer time to start showing results, but within 4 weeks you should start seeing some improvement.
You should also apply a moderate amount of the blend because the skin will absorb as much as it needs, the rest would simply be wasted.
As for the hot packs, I haven’t tried them yet but the principle is the same as for hair growth. Hot packs keep the area where they’re wrapped around warm/hot so that the oils can penetrate deeper into the skin.
When you apply hair masks (Peppermint oil + Castor oil/Coconut oil) for hair growth and other benefits, you’re advised to warm the blend before applying it, and then use a shower cap to keep the heat inside for about an hour before you wash it off. Warm environments open up the pores and the skin gets more nutrients and essential fatty acids from blends and work a bit faster.
I hope this helps, best of luck to you