Visa application for tourist visa in Beijing

Hello
I am Argentina's passport holder and I am now in South Korea in a touristic travel. I want to make a travel to Beijing but in the travel agency here they told me it's not possible to get the visa (since I don't have any registration card). But they recomended me to go to Hong Kong and get the visa there. So, if I go to Hong Kong with my plane ticket Hong Kong-Beijing already booked and the tour in Beijing also booked, how long does it take to get the visa? Is there any other requirements to get the visa there? I ask because it's a risk to have everything already booked (and paid) and then there are more problems with the visa...