I have got schengen visa which expires on Feb 19. What if I start my journey on Feb 19?

You won't be able to travel. when you're going somewhere where you need a passeport or a visa, the expiration date must be at least 6 months later than the departure

Not possible.....i dont think that it is possible that u will be allowed to travel the same day your visa expires...

U will simply be refused at the deprting airporrt.. In case they make a blunder you will be deported abck from your destination....

so dont take risk...

then your visa will be out of date and you will not be allowed across borders. They most likely not allow you entry because the visa has only 24 hours on it

You need to get another visa in order to ensure entry to Shenzen China and remain there - what you intend to do is not feasible - you will not gain entry.