The drying time of paint depends on the type of paint, the ratio of pigment to binder and environmental conditions. Latex and enamel paints dry faster than oil-based paints and may be dry to the touch in as little as an hour.
Latex and enamel paints dry faster than oil-based paints because they're water-based and dry through evaporation of the water from the mix of pigment and polymer molecules that binds to the surface being painted. Oil-based paints also go through evaporation, but their binders also go through chemical reactions to create long-lasting polymers. This slows drying time. All paints dry better when humidity is low, ventilation is good and temperatures are above 50 degrees Fahrenheit.