Four minutes is the standard French press steep time. It is the right answer for most coffees and most drinkers. The interesting part is what you do before, during, and after those four minutes.
The four-minute method
Use a 1:15 ratio: 30g coffee to 450g water for a typical press. Coarse grind, the texture of breadcrumbs. Pour all the water in one steady motion, start a timer, and let it sit for four minutes.
At the four-minute mark, break the crust on top with a spoon. Skim off the foam and floating grounds. Wait another two to three minutes. Then plunge slowly and pour.
Why the wait after breaking
Plunging immediately after stirring forces fines and fragments through the mesh, ending up in your cup as muddy sediment. The two to three minute settling period after breaking the crust lets most of those particles sink to the bottom, leaving a cleaner cup when you finally plunge.
What changes with steep time
Shorter steeps (3 minutes) give you a brighter, lighter cup. Longer steeps (5-6 minutes) extract more body and bitterness. Both are valid; both depend on your beans and your taste. With a darker roast, you may prefer 3 minutes to avoid harshness. With a lighter roast, 4 to 5 minutes draws out more sweetness.
Common mistakes
Grinding too fine clogs the mesh and produces sludge. Plunging too fast forces fine particles through. Using water that is off the boil (around 95 degrees Celsius is ideal, not 100) prevents over-extraction of bitter compounds.