25 hours layover at Bejing

Harry, since the layover is longer than 24 hours, you will have to obtain a Chinese transit (G) visa in advance. This type of visa is tied to your flight itinerary and the entire length of your stay in China cannot surpass roughly 7 days. Please, be careful because if you ask for more days, you are running a risk to be forced to apply for a tourist (L) visa that is somewhat more complicated to obtain. I would advise you not to go over 3 days when using a transit visa. So, plan your flights accordingly. By the way, the usual fees for a transit visa are practically the same as for a tourist visa. You should check what it is the situation with a Chinese visa in Vietnam.

Thanks Borut for your reply!
I looked up on google and saw the temporary permit sticker for 24 hour visa free transit like for example: Date of entry 01/04 - Stay until 02/4 (no exact times on the sticker)
so let's say if I arrive at 10:15 on 01/04 and depart at 11:20 on 02/04. My temporary permit should be Date of entry 01/04 - Stay until 02/04. Does that mean until 23:59 on 02/04? and I don't need a transit visa because I depart at 10:20 on 02/04? or they won't issue me a temporary permit because the layover is past 24-hour based on arrival and departure times on the boarding passes?
sorry it's still kind of confused to me.

Harry, unfortunately, you are not eligible for 24 hour visa free transit. Please, do not look at the stickers or similar because the real times are deposited in the computerized system. It is only the scheduled times that matter when we talk about 24 hour visa free transit. Also, the transit time is counted from the time of your scheduled arrival in China until the time of your scheduled departure from China. If the transit time, counted as I have explained, exceeds 24 hours just for 1 minute, you will be denied boarding the plane in Hanoi. Trust me, there was not any other explanation or interpretation from the one I have just presented. I'm really sorry, but you will have to obtain a Chinese transit (G) visa for this journey.