The short version: most modern water-based emulsions are touch-dry in an hour and recoatable in 2-4 hours. But don't treat that as gospel — the recoat window depends as much on your room as it does on the paint.
For standard matt emulsion — Dulux, Crown, COAT, Lick, Little Greene Intelligent Matt — 2-4 hours is bang on. F&B's Estate Emulsion and Modern Emulsion sit in the same bracket. The mistake people make is rushing the second coat because the surface feels dry. A film can feel dry on top while still soft underneath, and dragging a roller over it lifts the first coat right off. Patience saves you a redo.
Oil-based and traditional finishes are a different game. Anything with linseed or alkyd in it — eggshell, gloss, Edward Bulmer's natural paints, some Mylands and Sanderson oil-based trim — wants a proper overnight cure. Reckon on 6-16 hours, and don't be tempted to push it. Oil dries by oxidation, not evaporation, so warm and well-ventilated helps, but it won't be hurried.
The big variables are temperature and humidity. A cold, damp room in January will double your drying times whatever the tin says. Aim for 10°C minimum, ideally 15-20°C, with a bit of airflow. Crank a dehumidifier in a bathroom or a freshly plastered room if you're struggling. Conversely, baking heat and direct sun aren't your friends either — paint that skins too fast can trap solvent and craze.
If you're using a primer like Zinsser BIN, that's shellac-based and recoats in around 45 minutes, which is why decorators love it for a quick turnaround.
Practical advice: always read the recoat time on the actual tin, set a timer, and if in doubt, give it longer. Half an hour of waiting beats a day of stripping a botched second coat.