in-game help > contents > fighting > Real time duel against other players:
Real time dueling also consists of rounds. The quicker player can hit every 15 seconds, while the slower player will have to wait more than 15 seconds between hits.
i've noticed occationally with a high-quick char, i sometimes appear to get wait times less than 15 seconds. but after taking a closer look at it, it seems i didn't attack immediately when i could the previous 'round', so the amount of time waited was already deducted from the 15 seconds from the next round.
another possibility is that i heard a rumour (was a usually reliable source, at the time) that the initial times are calculated based on quick/luck of each char, but then after the first round, those times are adjusted, to account for the advantage of who got first attack. now, while that seems possible, i don't believe it would be true because it's more complicated than most things are in this game, as far as i have noticed. but that's not to say that isn't the case. i don't really know.
--jason