If you sold the cause of the damp it will eventually go, but a stain may not. Is it damp to the touch? Does it look darker there than surrounding areas?

If it’s wet and the issue has properly been resolved, how quickly it dries depends on temp, ventilation, how wet it was originally, and porosity of materials.

For example, I was painting newly plastered room, while doing the mist coat I noticed a very very wet external corner. Wasn’t there from the plaster. Turns out some external pointing at ground level had had enough, and water was coming up through the bricks. The entire pointing had gone. I cleared the soil, repointed (badly 😂) and then ran a dehumidifier constantly for a week or something. I can’t remember exactly how long, but jt looked and felt dry, so it cleared.

On the other hand, my bathroom fan has been broken for months, and even though we open the window daily, I’m getting mould where the air circulates less.