Irish passport holder transit in Shenzhen airport

Aaron, do you intend to travel to Hong Kong or Macau after your stay in Shenzhen. I'm asking you this for the sake of defining the best option that could be offered to you. For example, 24 hours visa free transit in Shenzhen is not particularly usable because you cannot exit to Macau or Hong Kong. Anyway, 144 hours visa free transit is ideal for that because it's free and allows you to travel all over the Guangdong province. After that you can exit to Macau and Hong Kong by ferry. Of course, to be eligible for 144 hours visa free transit in Shenzhen, you are required to stay in Shenzhen for at least 25 hours.

Thank you Zupan.

I will travel on a connecting flight to Japan first. Then on my way back I will travel from japan and stay for 4 days and hope to travel to Hong Kong if possible.

Is it possible to get a 24 hour when I travel first for the connecting flight? And then 2 weeks later when I come back get the 144 hour visa?

Yes, you can. So, you have to keep in mind that during your first itinerary you have to fly from some other country to Shenzhen and then to Japan:

X country (different than mainland China and Japan) - Shenzhen - Japan

As you have mentioned, your stay will be just a short transit, so you can be definitively covered by 24 hours visa free transit.

After your stay in Japan your itinerary will be, If I'm not wrong:

Japan - Shenzhen - Hong Kong

This itinerary is eligible for 144 hours visa free transit, but you will have to book your ferry ticket online in advance through CKS - Chu Kong Passenger Transport Company website. You will present your ticket already in japan at check-in and also after you land in Shenzhen. You should keep in mind that you will have to travel by exactly that ferry you have bought your ticket for.