Which time in Yangshuo downtown?

Oh no! That's not right, I have to be at 12:00 at station Guilin (also South)...

So, on which time is the first express bus to Guilin South? :) Thanks for your help!

Well, I suppose your schedule is Yangshuo-Guilin-Beijing? The bus line go from downtown to the railway station taking about 1 hour. Then you take a high speed ride to Guilin North Station and transfer to Guilin Railway Station by bus or taxi, around 40 or 50min for a ride to Beijing at 12:09. Taking the waitng time, time for ticket collection etc into consideration, you may need to depart before 8am. There should be a bus from downtown Shima Yuanpan around 7:30am. This may work for you. You'd better to double check this schedule once you get there as the schedule may changes in different season.

Thanks a lot!

Would it not be better to take a bus from Yangshuo to Guilin (South) directly?

There is no Guilin south railway station. If by bus to Guilin directly, it is better to go to Guilin North Bus Center which is closer to Guilin North Station. There should be bus available, but not clear the schedule. You need to ask the local people there. If not, you can only take a bus to the main bus station in Guilin and then go for GUilin North station.