This is where a lot of people come unstuck. Eggshell feels hard after a day or two, but that's not the same as cured. Paint cures through a chemical cross-linking process that continues long after it feels dry to the touch, and wiping down too early — even with a damp cloth — can leave dull patches, drag marks, or lift the surface.
The rule of thumb: leave eggshell at least 2–4 weeks before any serious cleaning. In colder rooms or during winter, push that to 4–6 weeks. Heat, ventilation, and humidity all affect the cure rate.
This applies across oil-based and water-based eggshells alike, though there are differences. Traditional oil-based eggshell — the kind Farrow & Ball's Modern Eggshell is modelled on in terms of sheen — cures harder and more durable in the long run, but it's actually slower to fully harden in those early weeks. Water-based eggshells like Little Greene's Intelligent Eggshell or Mylands' Eggshell dry faster but are similarly vulnerable to marking before the cure is complete.
If you absolutely must wipe something down sooner — say, you've got a splash or a mark — use a barely-damp cloth and blot rather than rub. Test in an inconspicuous spot first. The flatter the sheen, the more visible any damage will be.
On woodwork and joinery especially, where eggshell sees daily contact, patience here really does pay off. Rushing the cure is one of the most common reasons a job that looked great on the day ends up looking tatty inside a month.
Practical advice: if you're painting kitchen cabinets or a bathroom door, schedule the job so it gets 4 weeks of low-contact time before it goes back into heavy use. Tape a note to the surface if you need to — it sounds daft but it works.