jjwritergirl, After a bath/shower is preferable, but also before bed. Applying as often as possible is best. It's all natural, you can't really overdo it.
I use coconut oil on my feet when they get really bad. I sometimes make a scrub with that and sugar to use during the shower. It makes them very soft. Before bed lotion with saran wrap then socks on afterwards just in case lotion gets out of the saran wrap. I only do that a few times a year when I feel they are getting bad!
When my feet get really bad and start to crack I use something called Blue Goo, it's emu oil and beeswax. It cured the cracks in a few days. I bet it would help dry skin too. I got it at walmart in the foot care section in a little blue tin.