It would be foolish to say when the altcoins session will end. No one can say for sure about the future of cryptocurrency. There are many experts who have set 2021 for halving altcoins, but it is difficult to say how reasonable that is. But in this case, waiting is just a matter of time.
Thats true, we cant certainly predict when or for how long this bullish season will last. We can make a prediction but there's no guarantee that it can happen in the future.
Currently most coins are moving upward together with bitcoin, a time to take profit for long period hodlers.
So instead of thinking of the bullish season ending, better to think of wise decision at the moment and take advantage the market.