A manicure that feels dry to the touch and then dents an hour later has usually been applied too thickly. The cause is how polish hardens rather than how long it was left.
Polish dries by evaporation, not curing
Conventional nail polish is a mixture of film-forming polymers, pigments and plasticisers dissolved in volatile solvents.
Hardening happens as those solvents evaporate into the air, leaving the polymers behind as a continuous solid film on the nail.
No chemical reaction is involved, which is the fundamental difference from gel polish, where light triggers a reaction that hardens the product throughout.
Evaporation only happens at the surface
Solvent can only leave from the exposed top of the layer, so drying proceeds downward from the surface rather than uniformly through the coat.
As the top hardens it becomes a barrier, and solvent trapped beneath must diffuse through the forming film before it can escape.
The thicker the coat, the further that solvent has to travel and the more effectively the surface film blocks its route out.
Why the surface lies about the state underneath
A thick coat develops a firm skin within minutes while the material beneath remains liquid, so touching it lightly gives a misleading impression.
Any pressure applied after that point deforms the soft layer, and the surface film moves with it, leaving the dents and smudges characteristic of thick application.
Two thin coats reach a fully solid state far sooner than one thick coat, because each has a short distance for solvent to travel.
What quick-dry products do
Quick-dry topcoats generally use faster-evaporating solvents and film formers that set rapidly, hardening the surface sooner.
Drying drops work differently, spreading an oil across the surface that helps solvent escape and reduces the tackiness that catches on things.
Neither accelerates evaporation from deep within a thick coat, so both improve the surface without solving the underlying problem.
Conditions change the timing
Warm air holds more solvent vapour and speeds evaporation, while cold air slows it, which is why polish applied in a cold room takes noticeably longer.
High humidity slows the process and can cause a hazy finish as moisture is drawn into the film while it sets.
Cold water is sometimes used to firm the surface quickly, though it hardens only the outer film and leaves the interior in the same state as before.
Older polish thickens as solvent escapes through the cap over time, and the thicker liquid applies as a heavier coat, which reproduces the same problem from the bottle onwards.