Shenzhen visa ( Vietnamese passport)

The first and the most important detail is that you are definitely eligible for 24 hour visa free transit because you are exactly in a minute within the 24 hour time frame and you do not need any kind of visa. Also, it is the scheduled time that matter and not the real one because your departing flight could be delayed and your arrival flight could arrive ahead of time. So, you should not bother yourself about these details.

As far as temporary entry permit is concerned, you should be aware that the issuing of one always depends on the discretionary right/decision of the immigration staff. In any case, having such a long layover and if you decide to book a simple accommodation, that will almost guarantee that your permit will be granted.