how long it takes for mold to grow to became a problem?
I wish I could give you an answer, but really, there is no set length of time. It varies for several reasons.
Different species of mold grow at different rates of speed and even that is different under different growing conditions.
People respond uniquely to mold. It depends on the level of mycotoxin produced, and the degree of immune response. What is more important is to remember how allergies work. Exposure tends to lead to allergic response.
If there has been some kind of flood, and the conditions are ripe for mold to grow, it is crucial to eliminate the favorable conditions for mold growth as soon as possible. Mold can gain a significant foothold in as little a 24 hours. Don’t wait around for it to a become life-threatening issue.