Meanwhile, I would suggest that anyone trading on smaller exchanges should take all their money out of the exchange when they have finished trading rather than leaving large amounts of money on the exchange.
Better: Don't use such unknown exchanges at all.
If the exchange is a scam and wants to steal your funds, they don't need you to keep your funds for a long time there. All they need is that you make a deposit.
You're absolutely right, if the exchange has been established with the sole purpose of defrauding users right from the start, then they don't have to wait for months or years to defraud anyone of their money. Immediately you deposit your coins into their platform, then your funds is practically at their mercy.
The tricky part is, not all scams are easy to spot. Some platforms seem legit at the beginning, make you go through the withdrawal process for a while and gain your trust before issues begin to arise. Which is why it's best to choose trusted exchanges and always avoid leaving big amount of money in any exchange.