TravelDream

What's your plan there? If you're looking for natural beauty, Yangshuo is the place to go. It's about an hour from Guilin.
Yangshuo is a stunningly beautiful place and I couldn't recommend it more.
I've been there in August and it is very hot - but it wasn't that unbearable and the humidity was lower than Hong Kong. That said, I wouldn't plan days of bicycle riding unless your very used to extreme heat.
I've never taken the train as I flew with Cathay Dragon. If you're worried about price, check out Cathay's FanFares page as Guilin comes up quite regularly. I flew using British Airways Avios (4500 Avios + £13 each way).

I have though been to Shenzhen North station and it can be a pain.
It takes 60+ minutes to get from HK island to Lok Ma Chau.
The border takes X minutes long. If I had pre-booked tickets, I would allow, at an absolute minimum, 60 minutes. Double that if it's a holiday. You could do it in 15 though. I have found Lo Wu quicker as they have a separate queue for foreigners so you may want to consider there if it's a holiday.
It then takes 30 minutes to get from Lok Ma Chau to Shenzhen North station. I have always found Chinese train stations to be pretty manic and Shenzhen North WILL be manic throughout the holiday period (July and August). 60 minutes would be the absolute minimum I would allow to collect tickets. 120 minutes is more realistic to grab tickets and find the boarding area.
As you can see, five hours after leaving the hotel, you have just collected your tickets. Not a quick or easy journey.

I'm sure someone will jump in and say that they've done it in three hours. Possible? Perhaps - though not for a normal human on a normal day.


For the flight, I would plan to be on the train in HK station about 75 minutes before departure time if I had only hand luggage.