UltraVNC

Do you mean it can't even be changed by modifying and recompiling the sources??

Well, I have nothing against modifying the source code. Any pointer about which bit of it? I mean, any indication about which part of it?

Has anybody any idea how to change the 5-minutes limit SC waits for a connection? I have even tried looking at the sources, but I just can't find any mention of a 300000 ms value.
Any help would be appreciated.

The prompt is not in SC, but in the viewer. I had the same problem and eliminated it by commenting about 10 lines of code and then recompiling; if you want, I can send you the modified version of the viewer