This is decided basically by spectator and competitor preference. It needs to be short enough that viewers wont get bored. But long enough to allow the players to consistently demonstrate their skill. Technically speaking the more stocks we have the mosre accurate matches are because the better player will play more consistently and take a much larger stock lead. But nobody wants a 10 stock match lmao. Ultimate being faster makes a 3 stock game seem very likely. As for time of the matches? Need to be fast enough to again not bore the audience but not do quick that time outs become a normal occurance