In all decisions, timing is very important.
We may have the best idea, the greatest conclusion and the most effective strategy in mind. That's really possible. The next most important thing to consider is the timing.
When to decide? It's up to you. You may be too early or too late. Sometimes, it's really impossible to hit the perfect timing. If you did, congratulations.
If you are to make a decision, think how it will affect your present and future. Dig your past experiences and evaluate them to guide you to have the right decision.
How could you know if it's the right time? I believe a door will be opened. When you started to see the opportunity rather the negative probabilities, make a decision. Just make sure your decision is right if you have the right timing.
Test yourself. When is the best time to...
...propose to marry your girl?
...shift your career?
...eat ice cream - when you are happy or depressed?
...buy a (an expensive) laptop computer?
...become an entrepreneur?