Depends on how good your skill and how experienced you are with trading, if you got a good skill then you can earn in a day, but sometimes you need more than a month before you can earn profit, the most important to know what coins to buy and to trade
How long does a trade take?
It depends on what kind of trader you are, if you are a day trader a trade will last anything from a few hours to some minutes, if you prefer to trade long term then a trade could last weeks months or even years, there are many people that hold bitcoin since the beginning and have not sold their coins, so that means they have maintained their positions for almost a decade.
It depends on how you trade, as of this now in bitcoin we see our market is consistent in increasing. They continues to pump, this is a great opportunity to every one especially who has a big value of bitcoin.
Since the bitcoin price are not stable they have a sure profit, just need to wait the rigth time for the right price. We can't predict that event but reading and making idea through others will help to make a decision for trading.
I think much better to trade in the long period of time just like the past month, the price is almost $1k and now it reach $2k. This is a luck happenings in a professional trader.