i just want to add something to this point. part of the risk is not a matter of length of time, it is the matter of storing coins on exchanges. in other words when you are depositing your coins on an exchange even for a single second, as soon as that deposit is confirmed you are at risk of losing your money. the exchange can scam you that very instant.
which is why if you want to start trading, you should also consider this risk among other risks involving trading.