How quickly will water damage take effect?

Some effects of water can take place very quickly. Some immediate effects can include damage to electrical appliances and wiring. Electrical appliances can begin to malfunction, sometimes in dangerous ways, and circuits not wired to protect against it can begin shorting out. Within a few hours, you will notice that porous materials like drywall, paper, wood, and carpeting can absorb significant water amounts. Wood furniture might start to swell and crack.
Within the first few days, mold and other microorganisms can start to grow. The air will start to smell foul, and it may have significant toxicity. Drywall can bulge and break. Metals will start to corrode, superficially at first.
Within a week, mold and other microorganisms will spread through the property. Wood structural components can start to warp, including windows and doors. Significant corrosion will be evident on metals. By this point, the structural integrity of metal components may begin to degrade. The structure may soon be too unstable to occupy safely.