For a day-trader seeking to buy a coin at a low price, you should not wait longer than a week. If the coin does not fall as low as desired, either raise your price or move to another coin.
Time is a key factor in trading... you measure profit in terms of how long it took you to earn it.
But when you are stuck with a dead coin sometimes you might have to wait a bit longer for a price rise, if not, accept defeat, sell and move on.