First thing you need to understand is there is no fixed time to startup, as soon as you get a good idea you should immediately start working on it, by working I mean just follow the necessary steps needed for building the startup.
The more you think for the best time to start the business the more you will face competition from the market.
Apart from all the these things, the question that you have asked mainly arises when looking at the financial status, generally one think that first get some financial security after that we would we can go for startup, which is completely OK to have this thought.
Now here comes your decsscion making abiltyi, let us say, you got some nice and kickass idea but the finance required to make it is huge, so what you can do is to first try to get review about your idea from your peers, friend, etc.
Try to submit your application in various accelerators and incubation platform, if you get selected in this, they will guide you to build your venture also you will have a nice exposure.
If this thing failed then it is sure that your idea need more furnishing, and then you should work on it with your studies and test your idea at certain phases.
see, there is no such word as "security" for an entrepreneur, those who wish to be has to take risk at some point or other.
there are some points to have on your check list:
1). Am I be able to take risk?
2). What will be its impact on my life, it works or if it not?
3).What are the financial risks associated with it?
4).Will I be able to take financial risk?
5). Do I have confidence on my product?
Have a answer to these points and then decide what you want to do.