In that case you could calculate how much did you spend in electricity/gas depending on your oven.
The way you organize your time is up to you; in my case, also a home baker (learning still, without a steady number of monthly orders), I try to clear up while I have a cake in the oven, but that doesn't mean I wont be clearing up again after the cake has been decorated. I try to make an estimate. For me it's easier to price a slice, that will depend on the type of cake and decoration. It is good to have an idea of this prior to any consultation with a client. Also, if you're a hobbyist you may be doing this on your spare time after work, like I do, I organize a single cake days ahead of the actual making. I usually won't take an order with less than 2 weeks notice, so I can organize each day of the week I will be delivering that cake.
So perhaps, for "time" you could consider:
1.- Consultation & Design time
2.- Shopping time
3.- Cake making time (Baking, Decorating, Figurine modeling <-- these, price them ahead of time, etc) -*yikes, it all takes time!*
4.- Clearing up time
5.- Delivery cost, if you're doing that yourself.
Maybe you should read Jason's blog, he discusses about Pricing and breaks it all down very clearly.