Nobody knows - at least not for certain. No one can reliably predict how the financial markets will develop in the future. Consequently, the "perfect" times to get in and out only become clear in hindsight. Speculating on this often backfires, as you usually end up chasing market trends. 

Instead, it's advisable not to wait, but to start investing as early as possible - regardless of how the market seems at the moment. After all, the longer your investment horizon, the significantly lower the risk of loss becomes. Plus, you benefit more from the power of compound interest. 

Furthermore, it's advantageous in the long run to hold onto your investments through all market conditions. This is the strategy findependent follows. It requires perseverance during a crisis but ultimately leads to higher returns and minimized risk. 

The best approach is to automate your deposits with a standing order. That way, you don't have to think about it and won't be tempted to speculate on market timing.