1. Raw clay
You start a process of creating a ceramics piece from a raw clay, that you should knead properly .With this you remove all air bubbles (air bubbles can explode in the kiln).
From properly kneaded clay you can form your object.
Before firing, the clay should dry. During this process, it becomes fragile, and it shrinks a little bit. When a piece of pottery has dried completely it is called a greenware. It has no flexibility at all. But you can slow drying process: cover a clay in a piece of plastic. And even in a few day, while clay is still in leather-hard state, you can work with it, for example, trim the bottom (if you work with a wheel) or cut some decorative elements.
Drying will take from 1 day minimum (depends on a size of an item)
3. Bisque Firing
This firing is to approximately 600-700 degrees Celsius. This hardens the piece making it easier to handle without breaking during the glazing process. Clay fired at this temperature still can absorb a liquid, which will be helpful at a glazing stage.
Firing takes 1 day approximately.
You can think about glaze as a ground glass mixed with water (it’s more complicated, but it’s just to simplify the explanation). When you cover bisque fired clay with this mixture, water is absorbed in piece pores and the glass stays at the top. Glass will be melted in a kiln, so the bottom of an item should be cleaned of glaze. You can see even in shop’s ceramics that the bottom is not covered and looks more natural
This firing takes longer (approx 1.5 days) because of a temperature twice higher 1000- 1250 degrees. This is the final step (overglaze firing could follow this one, but it's for some techniques)
This firing takes more than 1 day.
The fastest when you can make a ceramics is 3 days. But nobody fire one separate object. Ceramics kiln consumes a lot of electricity, so you should be sure that it is spent rationally and an oven is fully loaded. My process from a clay to ready object takes a month.
At the picture at the start you can see that ready object is smaller that a raw object. Shrinkage occurs due to the loss of water. The finer the particle size of the clay, the more water layers, hence the more shrinkage.
Image source: https://quizlet.com/239960842/stages-of-clay-diagram/