As with everything, this depends on the person. Some women report their stomachs getting firmer toward the end of their first trimester. Most common seems to be stomach hardening at about 18-28...
Basically they don't. A clarification of terms. Decompose is usually reserved for organic materals being educed by microorganisms. A drink can is made of metal so t is not attacked by microorganisms....
Assuming an empty stomach, about 20 minutes. However, while it is in the stomach, about 30% will be absorbed through the stomach wall. The rest will be absorbed from the small intestine.